Christianity is a cheerful religion and brings joy and peace from heaven to earth. The New Testament opens with the gospel, that is with the authentic record of the history of all histories, the glad tidings of salvation through the life, death, and resurrection of Jesus Christ.  The four canonical Gospels are only variations of the same theme, a fourfold representation of one and the same gospel, animated by the same spirit.  They are not full biographies,  but only memoirs or a selection of characteristic features of Christ's life and work as they struck each Evangelist and best suited his purpose and his class of readers.  They are not photographs which give only the momentary image in a single attitude, but living pictures from repeated sittings, and reproduce the varied expressions and aspects of Christ's person.
The style is natural, unadorned, straightforward, and objective. Their artless and naïve simplicity resembles the earliest historic records in the Old Testament, and has its peculiar and abiding charm for all classes of people and all degrees of culture. The authors, in noble modesty and self-forgetfulness, suppress their personal views and feelings, retire in worshipful silence before their great subject, and strive to set it forth in all its own unaided power.
The first and fourth Gospels were composed by apostles and eye-witnesses, Matthew and John; the second and third, under the influence of Peter and Paul, and by their disciples Mark and Luke, so as to be indirectly likewise of apostolic origin and canonical authority. Hence Mark is often called the Gospel of Peter, and Luke the Gospel of Paul.
The common practical aim of the Evangelists is to lead the reader to a saving faith in Jesus of Nazareth as the promised Messiah and Redeemer of the world. 
The Gospels have their common source in the personal intercourse of two of the writers with Christ, and in the oral tradition of the apostles and other eye-witnesses. Plain fishermen of Galilee could not have drawn such a portrait of Jesus if he had not sat for it. It would take more than a Jesus to invent a Jesus. They did not create the divine original, but they faithfully preserved and reproduced it.
The gospel story, being constantly repeated in public preaching and in private circles, assumed a fixed, stereotyped form; the more readily, on account of the reverence of the first disciples for every word of their divine Master. Hence the striking agreement of the first three, or synoptical Gospels, which, in matter and form, are only variations of the same theme. Luke used, according to his own statement, besides the oral tradition, written documents on certain parts of the life of Jesus, which doubtless appeared early among the first disciples. The Gospel of Mark, the confidant of Peter, is a faithful copy of the gospel preached and otherwise communicated by this apostle; with the use, perhaps, of Hebrew records which Peter may have made from time to time under the fresh impression of the events themselves.
But with all their similarity in matter and style, each of the Gospels, above all the fourth, has its peculiarities, answering to the personal character of its author, his special design, and the circumstances of his readers. The several evangelists present the infinite fulness of the life and person of Jesus in different aspects and different relations to mankind; and they complete one another. The symbolical poesy of the church compares them with the four rivers of Paradise, and with the four cherubic representatives of the creation, assigning the man to Matthew, the lion to Mark, the ox to Luke, and the eagle to John.
The apparent contradictions of these narratives, when closely examined, sufficiently solve themselves, in all essential points, and serve only to attest the honesty, impartiality, and credibility of the authors. At the same time the striking combination of resemblances and differences stimulates close observation and minute comparison, and thus impresses the events of the life of Christ more vividly and deeply upon the mind and heart of the reader than a single narrative could do. The immense labor of late years in bringing out the comparative characteristics of the Gospels and in harmonizing their discrepancies has not been in vain, and has left a stronger conviction of their independent worth and mutual completeness.
Matthew wrote for Jews, Mark for Romans, Luke for Greeks, John for advanced Christians; but all are suited for Christians in every age and nation.  The first Gospel exhibits Jesus of Nazareth as the Messiah and Lawgiver of the kingdom of heaven who challenges our obedience; the second Gospel as the mighty conqueror and worker of miracles who excites our astonishment; the third Gospel as the sympathizing Friend and Saviour of men who commands our confidence; the fourth Gospel as the eternal Son of God who became flesh for our salvation and claims our adoration and worship, that by believing in him we may have eternal life. The presiding mind which planned this fourfold gospel and employed the agents without a formal agreement and in conformity to their talents, tastes, and spheres of usefulness, is the Spirit of that Lord who is both the Son of Man and the Son of God, the Saviour of us all.
Time Of Composition.
As to the time of composition, external testimony and internal evidence which modern critical speculations have not been able to invalidate, point to the seventh decade of the first century for the Synoptic Gospels, and to the ninth decade for the Gospel of John.
The Synoptic Gospels were certainly written before a.d.70; for they describe the destruction of Jerusalem as an event still future, though nigh at hand, and connect it immediately with the glorious appearing of our Lord, which it was thought might take place within the generation then living, although no precise date is fixed anywhere, the Lord himself declaring it to be unknown even to him. Had the Evangelists written after that terrible catastrophe, they would naturally have made some allusion to it, or so arranged the eschatological discourses of our Lord (Matt.24; Mark 13; Luke 21) as to enable the reader clearly to discriminate between the judgment of Jerusalem and the final judgment of the world, as typically foreshadowed by the former. 
On the other hand, a considerable number of years must have elapsed after the resurrection. This is indicated by the fact that several imperfect attempts at a gospel history had previously been made (Luke 1:1), and by such a phrase as: "until this day" (Matt.27:8; 28:15).
But it is quite impossible to fix the precise year of composition. The silence of the Epistles is no conclusive argument that the Synoptists wrote after the death of James, Peter, and Paul; for there is the same silence in the Acts concerning the Epistles of Paul, and in the Epistles concerning the Acts. The apostles did not quote each other's writings. the only exception is the reference of Peter to the Epistles of Paul. In the multiplicity of their labors the Evangelists may have been engaged for several years in preparing their works until they assumed their present shape. The composition of a life of Christ now may well employ many years of the profoundest study.
The Hebrew Matthew was probably composed first; then Mark; the Greek Matthew and Luke cannot be far apart. If the Acts, which suddenly break off with Paul's imprisonment in Rome (61-63), were written before the death of the apostle, the third Gospel, which is referred to as "the first treatise" (Acts 1:1), must have been composed before a.d.65 or 64, perhaps, in Caesarea, where Luke had the best opportunity to gather his material during Paul's imprisonment between 58 and 60; but it was probably not published till a few years afterwards. Whether the later Synoptists knew and used the earlier will be discussed in the next section.
John, according to the universal testimony of antiquity, which is confirmed by internal evidence, wrote his Gospel last, after the fall of Jerusalem and after the final separation of the Christians from the Jews. He evidently presupposes the Synoptic Gospels (although he never refers to them), and omits the eschatological and many other discourses and miracles, even the institution of the sacraments, because they were already sufficiently known throughout the church. But in this case too it is impossible to fix the year of composition. John carried his Gospel in his heart and memory for many years and gradually reduced it to writing in his old age, between a.d.80 and 100; for he lived to the close of the first century and, perhaps, saw the dawn of the second.
The Gospels make upon every unsophisticated reader the impression of absolute honesty. They tell the story without rhetorical embellishment, without any exclamation of surprise or admiration, without note and comment. They frankly record the weaknesses and failings of the disciples, including themselves, the rebukes which their Master administered to them for their carnal misunderstandings and want of faith, their cowardice and desertion in the most trying hour, their utter despondency after the crucifixion, the ambitious request of John and James, the denial of Peter, the treason of Judas. They dwell even with circumstantial minuteness upon the great sin of the leader of the Twelve, especially the Gospel of Mark, who derived his details no doubt from Peter's own lips. They conceal nothing, they apologize for nothing, they exaggerate nothing. Their authors are utterly unconcerned about their own fame, and withhold their own name; their sole object is to tell the story of Jesus, which carries its own irresistible force and charm to the heart of every truth-loving reader. The very discrepancies in minor details increase confidence and exclude the suspicion of collusion; for it is a generally acknowledged principle in legal evidence that circumstantial variation in the testimony of witnesses confirms their substantial agreement. There is no historical work of ancient times which carries on its very face such a seal of truthfulness as these Gospels.
The credibility of the canonical Gospels receives also negative confirmation from the numerous apocryphal Gospels which by their immeasurable inferiority and childishness prove the utter inability of the human imagination, whether orthodox or heterodox, to produce such a character as the historical Jesus of Nazareth.
No post-apostolic writers could have composed the canonical Gospels, and the apostles themselves could not have composed them without the inspiration of the spirit of Christ.
1. The Symbolism of the Gospels. This belongs to the history of Christian poetry and art, but also to the history of exegesis, and may be briefly mentioned here. It presents the limited recognition of the individuality of the Gospels among the fathers and throughout the middle ages.
The symbolic attributes of the Evangelists were suggested by Ezekiel's vision of the four cherubim which represent the creation and carry the throne of God (Ez.1:15 sqq.; 10:1 sqq.; 11:22), and by the four "living creatures" (zoa, nottheria, "beasts," with which the E. V. confounds them) in the Apocalypse (Rev.4:6-9; 5:6, 8, 11, 14; 6:1, 3, 5, 6, 7; 7:11; 14:3; 15:7; 19:4).
(1.) The theological use. The cherubic figures which the prophet saw in his exile on the banks of the Chebar, symbolize the divine attributes of majesty and strength reflected in the animal creation; and the winged bulls and lions and the eagle-beaded men of Assyrian monuments have a similar significance. But the cherubim were interpreted as prophetic types of the four Gospels as early as the second century, with some difference in the application.
Irenaeus (about 170) regards the faces of the cherubim (man, lion, ox, eagle) as "images of the life and work of the Son of God," and assigns the man to Matthew, and the ox to Luke, but the eagle to Mark and the lion to John (Adv. Haer., III.11, 8, ed. Stieren I.469 sq.). Afterwards the signs of Mark and John were properly exchanged. So by Jerome (d.419) in his Com. on Ezekiel and other passages. I quote from the Prologus to his Comment. in Ev. Matthaei (Opera, vol. VII., p.19, ed. Migne): "Haec igitur quatuor Evangelia multo ante praedicta, Ezechielis quoque volumen probat, in quo prima visio ita contexitur: 'Et in medio sicut similitudo quatuor animalium: et vultus eorum facies hominis, et facies leonis, et facies vituli, et facies aquilae' (Ezech.1:5 et 10). Prima hominis facies Matthaeum significat, qui quasi de homine exorsus est scribere: 'Liber generationis Jesu Christi, filii David, filii Abraham' (Matth.1). Secunda, Marcum, in quo [al. qua] vox leonis in eremo rugientis auditur: 'Vox clamantis in deserto [al. eremo], Parate viam Domini, rectas facile semitas ejus' (Marc.1:3). Tertia, vituli, quae evangelistam Lucam a Zacharia sacerdote sumpsisse initium praefigurat. Quarta, Joannem evangelistam, qui assumptis pennis aquilae, et ad altiora festinans, de Verbo Dei disputat.
Augustin (De Consens. Evang., Lib. I., c.6, in Migne's ed. of the Opera, tom. III., 1046) assigns the lion to Matthew, the man to Mark (whom he wrongly regarded as an abbreviator of Matthew), the ox to Luke, and the eagle to John, because "he soars as an eagle above the clouds of human infirmity, and gazes on the light of immutable truth with most keen and steady eyes of the heart." In another place (Tract. XXXVI. in Joh. Ev., c.8, § 1) Augustin says: "The other three Evangelists walked as it were on earth with our Lord as man (tamquam cum homine Domino in terra ambulabant) and said but little of his divinity. But John, as if he found it oppressive to walk on earth, opened his treatise, so to speak, with a peal of thunder .... To the sublimity of this beginning all the rest corresponds, and he speaks of our Lord's divinity as no other." He calls the evangelic quaternion "the fourfold car of the Lord, upon which he rides throughout the world and subdues the nations to his easy yoke." Pseudo-Athanasius (Synopsis Script.) assigns the man to Matthew, the ox to Mark, the lion to Luke. These variations in the application of the emblems reveal the defects of the analogy. The man might as well (with Lange) be assigned to Luke's Gospel of humanity as the sacrificial ox. But Jerome's distribution of the symbols prevailed and was represented in poetry by Sedulius in the fifth century.
Among recent divines, Bishop Wordsworth, of Lincoln, who is in full sympathy with the fathers and all their pious exegetical fancies, has thus eloquently reproduced the cherubic symbolism (in his Com. on The New Test., vol. I., p. xli): "The Christian church, looking at the origin of the Four Gospels, and the attributes which God has in rich measure been pleased to bestow upon them by his Holy Spirit, found a prophetic picture of them in the four living cherubim, named from heavenly knowledge, seen by the prophet Ezekiel at the river of Chebar. Like them the Gospels are four in number; like them they are the chariot of God, who sitteth between the cherubim; like them they bear him on a winged throne into all lands; like them they move wherever the Spirit guides them; like them they are marvellously joined together, intertwined with coincidences and differences: wing interwoven with wing, and wheel interwoven with wheel; like them they are full of eyes, and sparkle with heavenly light; like them they sweep from heaven to earth, and from earth to heaven, and fly with lightning's speed and with the noise of many waters. Their sound is gone out into all lands, and the words to the end of the world." Among German divines, Dr. Lange is the most ingenious expounder of this symbolism, but he exchanges the symbols of Matthew and Luke. See his Leben Jesu, I., 156 sqq., and his Bibelkunde (1881), p.176.
(2.) The pictorial representations of the four Evangelists, from the rude beginnings in the catacombs and the mosaics of the basilicas at Rome and Ravenna to modern times, have been well described by Mrs. Jameson, Sacred and Legendary Art, vol. I, 132-175 (Boston ed., 1865). She distinguishes seven steps in the progress of Christian art: 1st, the mere fact, the four scrolls, or books of the Evangelists; 2d, the idea, the four rivers of salvation flowing from on high to fertilize the whole earth; 3d, the prophetic symbol, the winged cherub of fourfold aspect; 4th, the Christian symbol, the four "beasts" (better, "living creatures") in the Apocalypse, with or without the angel-wings; 5th, the combination of the emblematical animal with the human form; 6th, the human personages, each of venerable or inspired aspect, as becomes the teacher and witness, and each attended by the scriptural emblem -- no longer an emblem, but an attribute -- marking his individual vocation and character; 7th, the human being only, holding his Gospel, i.e., his version of the teaching and example of Christ.
(3.) Religious poetry gives expression to the same idea. We find it in Juvencus and Sedulius, and in its perfection in Adam of St. Victor, the greatest Latin poet of the middle ages (about 1172). He made the Evangelists the subject of two musical poems: "Plausu chorus laetabundo," and "Jocundare plebs fidelis." Both are found in Gautier's edition (1858), and with a good English translation by Digby S. Wrangham in The Liturgical Poetry of Adam of St. Victor, London, 1881, vol, II., pp.156-169. The first has been well reproduced in English by Dr. Plumptre (in his Com. on the Synoptists, in Ellicott's series, but with the omission of the first three stanzas). I will quote the third stanza of the first (with Wrangham's version):
Circa thema generale,
Habet quisque speciale
Quod praesignat in propheta
Forma pictus sub discreta
"Though one set of facts is statted,
They by each one are related
In a manner all his own:
This the prophet by four creatures,
Each of different form and features,
Pictures for us, one by one."
In the second poem the following stanzas are the best:
Formam viri dant Matthaeo,
Quia scripsit sic de Deo,
Sicut descendit ab eo,
Quem plasmavit, homine.
Lucas bos est in figura
Ut praemonstrat in Scriptura,
Hostiarum tangens jura
Legis sub velamine.
Matthew as the man is treated,
Since 'tis he, who hath related,
How from man, by God created,
God did, as a man, descend.
Luke the ox's semmblance weareth,
Since his Gospel first declareth,
As he thence the Law's veil teareth,
Sacrifice' aim and end.
Marcus, lleo per desertum
Clamans, rugit in apertum:
Iter fiat Deo certum,
Mundum cor a crimine.
Sed Johannes, ala bina
Forma, fetur in divinaa
Mark, the lion, his voice upraises,
Crying out in desert places:
"Cleanse your hearts from all sin's traces,
For our God a way prepare!"
John, the eagle's feature having,
Earth on love's twain pinions leaving,
Soars aloft, God's truth perceiving
In light's purer atmosphere.
Ecce forma bestialis
Quam Scriptura prophetalis
Notat, sed materialis
Haec est impositio.
Currunt rotis, volant alis;
Inest sensus spiuritalis;
Rota gressus est aequalis,
Thus the Thus the forms of brute creation
Prophets in their revelation
Use; but in their application
All their sacred lessons bring.
Mystic meaning underlieth
Wheels that run, or wing that flieth
One consent the first implieth,
Contemplation means the wing.
Quatuor decribunt isti
Quadriformes actus Christi:
Et figurant, ut audisti,
Quisque sua formula.
Natus homo declaratur
Leo mortem depraedatur,
Et ascendit aquila.
These four writers, in portraying
Christ, his fourfold acts displaying.
Show him - thou hast heard the saying -
Each of them distinctively;
Man - of woman generated;
Ox - in offering dedicated;
Lion - having death defeated;
Eagle - mounting to the sky.
Paradisus lis regature,
Viret, floret, foecundatur,
His abundat, his laetatur
Fons est Christus, hi aunt rivi,
Fons est altus, hi proclivi,
Ut saporem fontis vivi
These four streams, through Eden flowing,
Moisture, verdure, still bestowing,
Make the flowers and fruit there growing
In rich plenty kaugh and sing
Christ the cource, these streams forth sending;
High the source, these downward trending;
That they thus a taste transcending
Of life's fount to saints may bring.
Horum rivo debriatis
Sitis crescat caritatis,
Ut de fonte pietatis
Horum trabat nos doctrina
Vitiorum de sentinâ,
Sicque ducat ad divina
Ab imo superius.
At their stream inebriated,
Be our love's thirst aggravated,
More completely to be sated
At a holier love's full fount!
May the doctrine they provide us
Draw us from sin's slough beside us,
An to things divine thus guide us,
As from earth we upward mount!
II. The Credibility of the Gospels would never have been denied if it were not for the philosophical and dogmatic skepticism which desires to get rid of the supernatural and miraculous at any price. It impresses itself upon men of the highest culture as well as upon the unlearned reader. The striking testimony of Rousseau is well known and need not be repeated. I will quote only from two great writers who were by no means biased in favor of orthodoxy. Dr. W. E. Channing, the distinguished leader of American Unitarianism, says (with reference to the Strauss and Parker skepticism): "I know no histories to be compared with the Gospels in marks of truth, in pregnancy of meaning, in quickening power." ... "As to his [Christ's] biographers, they speak for themselves. Never were more simple and honest ones. They show us that none in connection with Christ would give any aid to his conception, for they do not receive it .... The Gospels are to me their own evidence. They are the simple records of a being who could not have been invented, and the miraculous and more common parts of his life so hang together, are so permeated by the same spirit, are so plainly outgoings of one and the same man, that I see not how we can admit one without the other." See Channing's Memoir by his nephew, tenth ed., Boston, 1874 Vol. II., pp.431, 434, 436. The testimony of Goethe will have with many still greater weight. He recognized in the Gospels the highest manifestation of the Divine which ever appeared in this world, and the summit of moral culture beyond which the human mind can never rise, however much it may progress in any other direction. "Ich halte die Evangelien," he says, "für durchaus ächt; denn es ist in ihnen der Abglanz einer Hoheit wirksam, die von der Person Christi ausging: die ist qöttlicher Art, wie nur je auf Erden das Göttliche erschienen ist." (Gespräche mit Eckermann, III., 371.) Shortly before his death he said to the same friend: "Wir wissen gar nicht, was wir Luther'n und der Reformation zu danken haben. Mag die geistige Cultur immer Fortschreiten, mögen die Naturwissenschaften in immer breiterer Ausdehnung und Tiefe wachsen und der menschliche Geist sick erweitern wie er will: über die Hoheit und sittliche Cultur des Christenthums, wie es in den Evangelien leuchtet, wird er nicht hinauskommen." And such Gospels Strauss and Renan would fain make us believe to be poetic fictions of illiterate Galilaeans! This would be the most incredible miracle of all.
 The Greek word euangelion which passed into the Latin evangelium, and through this into modern languages (French, German, Italian, etc.), means 1st, reward for good news to the messenger (in Homer); 2d, good news, glad tidings; 3d, glad tidings of Christ and his salvation (so in the New Test.); 4th, the record of these glad tidings (so in the headings of the Gospels and in ecclesiastical usage). The Saxon "gospel," i.e., God's spell or good spell (from spellian, to tell), is the nearest idiomatic equivalent for euangelion.  Irenaeus very properly calls them tetramorphon to euangelion, heni pneumati sunechomenon, quadriforme evangelium quod uno spiritu continetur. Adv. Haer. III. 11, 8.  This is expressly disclaimed in John 20:30; comp. 21:25  Hence Justin Martyr, in his two "Apologies" (written about 146), calls the Gospels "Memoirs" or "Memorabilia" (Apomnemoneumata) of Christ or of the Apostles, in imitation no doubt of the Memorabilia of Socrates by Xenophon. That Justin means no other books but our canonical Gospels by theme "Memoirs," which he says were read in public worship on Sunday, there can be no reasonable doubt. See especially Dr. Abbot's Authorship of the Fourth Gospel, 1880.  John 20:30, 31:tauta de gegraptai hina pisteuete oti Iesous estin Christos , ho huios tou theou, kai hina pisteuontes zeen echete en to onomati autou.  This characterization is very old, and goes back to Gregory Nazianzen, Carmen 33, where he enumerates the books of the New Test., and says; Mattheios men egrapsen Hebraiois thaumata Christou, Markos d Italie, Loukas Achaiidi Pasi d' Ioannes kerux megas , ouranophoites.  See on this subject Fisher's Beginnings of Christianity, ch. XI.: "Water marks of Age in the New Test, Histories," pp. 363 sqq., especially p. 371.
 Irenaeus very properly calls them tetramorphon to euangelion, heni pneumati sunechomenon, quadriforme evangelium quod uno spiritu continetur. Adv. Haer. III. 11, 8.
 This is expressly disclaimed in John 20:30; comp. 21:25
 Hence Justin Martyr, in his two "Apologies" (written about 146), calls the Gospels "Memoirs" or "Memorabilia" (Apomnemoneumata) of Christ or of the Apostles, in imitation no doubt of the Memorabilia of Socrates by Xenophon. That Justin means no other books but our canonical Gospels by theme "Memoirs," which he says were read in public worship on Sunday, there can be no reasonable doubt. See especially Dr. Abbot's Authorship of the Fourth Gospel, 1880.
 John 20:30, 31:tauta de gegraptai hina pisteuete oti Iesous estin Christos , ho huios tou theou, kai hina pisteuontes zeen echete en to onomati autou.
 This characterization is very old, and goes back to Gregory Nazianzen, Carmen 33, where he enumerates the books of the New Test., and says; Mattheios men egrapsen Hebraiois thaumata Christou, Markos d Italie, Loukas Achaiidi Pasi d' Ioannes kerux megas , ouranophoites.
 See on this subject Fisher's Beginnings of Christianity, ch. XI.: "Water marks of Age in the New Test, Histories," pp. 363 sqq., especially p. 371.