Haydock Catholic Bible Commentary
I saw four Angels, &c. Though some understand here evil spirits, whom God may make use of as instruments to punish the wicked, yet we may rather, with other interpreters, understand good angels sent from God to guard and protect his faithful servants both from evil spirits and wicked men. (Witham)
Having the seal. This sign is generally supposed to be the sign of the cross. In the East, it was the custom to impress some indelible mark upon the soldiers. This sign [the sign of the cross] amongst the ancient Christians was used on every occasion. (Calmet)
Hurt not the earth, &c. Some understand Christ himself, who gives his commands in this manner to the Angels; others, an Angel of a higher rank or order. --- Till we seal the servants of our God in their foreheads, which may be expounded, let not persecutions and trials come upon them till they are strengthened by the spirit and grace of God, with which St. Paul sometimes says the servants of God are signed and sealed. See 2 Corinthians i. 22.; Ephesians i. 13. He alludes to the passages of Ezechiel (Chap. ix. 4.) where God bids and angel mark with the letter Tau the foreheads of those who should not be hurt by the judgments that were to fall upon Jerusalem; so God would protect the faithful Christians, who believe and put their trust in Christ crucified, and who from the first ages [centuries], in testimony of this faith, used to sign themselves by making the sign of the cross on their foreheads, of which the letter Tau was a figure or resemblance. See Tertullian, de lib. Corona militis. I beg the readers patience, if I here set down what I find in the great Synopsis Papismi, in folio, put out by Mr. Andrew Willet, and dedicated first to queen Elizabeth, and afterwards to king James the first. Among his demonstrations, as he calls them, that the pope is the antichrist, (Controv. iv. q. 10. p. 232 and 233) he tells us in plain terms, "that the sign of the cross is one of the visible signs of antichrist. And who," saith he, "hath taught the papists that the sign of the cross is to be borne or made on men's foreheads? And that with crossing the forehead we are preserved from dangers? The superstitious marks of the cross had their beginning from the beast's name, since the number of the beast's name in the Revelation of St. John is by these Greek letters, Greek: chxs. The first letter, Greek: ch, is a cross; the middle letter, Greek: x, (in Latin, X) is also a side long cross; and the last letter, Greek: s, contains both Greek: s and Greek: t of which the latter is called a headless cross;" and then Mr. Willet concludes in these words, "And thus it plainly appears, that the marks whereby the papists say they honour Christ, are rather a dishonour to him, and are in very deed the cognizance of antichrist." Such an ingenious, and at the same time learned fancy, may perhaps outvie even those we have cited out of Mr. Brightman [in the annotations on Chap. iii. 14-22.], and may be equally serviceable to any country parson on the fifth of November, or on any day when he shall think fit to hold forth against the pope or popery. I suppose that Mr. Willet did not know that the Christians in the first ages [centuries] (as all Catholics to this day) made so frequent use of the sign of the cross, as it is witnessed by Tertullian above two hundred years before even any Protestant pretended that the popes began to be antichrists, or the great antichrist. And this, says he, they do by a tradition from father to son. At every setting forward or going about any thing, at coming home or going out, at putting on our clothes, at going to bathe, to table, to light a candle, to bed, to sit down, to any thing, we make the sign of the cross on our foreheads. And this is a tradition. The like is witnessed by St. John Chrysostom, St. Cyril of Jerusalem, and many of the Fathers. At the same time that with our hand we make the sign of the cross, we say these words, "in the name of the Father, and of the Son, and of the Holy Ghost;" the words used when any one is made a Christian, according to the command of Christ. So that the action itself puts us in mind that Jesus Christ died for us on the cross; and by the words, we make a profession of our Christian faith, that we believe in one God and three Persons. Can we do this too often? Dare we be ashamed of doing it? Was ever any thing more ridiculous than to call this in very deed the cognizance of antichrist? What must Mr. Willet have thought of the Protestants, or what can they think of him, and such like folio scribbers, to prove the popes the beast of St. John's Revelation? What must, I say, Mr. Willet think of the public liturgy, or the book of common prayer, approved and used by the Church of England in his time, and which ordains that the sign of the cross shall be made by the priest on the forehead of every one that is baptized? This, according to Mr. Willet, is (when any one is made a Christian) to give him the badge, and visible sign of antichrist, to the dishonour of Christ, and what in very deed is the cognizance of antichrist. (Witham)
I heard the number of them that were sealed. By these determinate numbers need only be understood a great number of Jews converted and saved, though much greater was the number of the saved taken from among the Gentiles of all nations, of which it is said, I saw a great multitude, which no man could number, &c. (Witham) --- The number of one hundred and forty-four thousand is not to be taken in a literal and strict sense, but to express in general terms the great number of the elect; for it appears that the tribe of Dan, which certainly must have produced some elect, is not mentioned, and the tribe of Joseph is put in lieu of that of Ephraim: so that if it be supposed that these numbers must be taken literally, the tribe of Joseph would have produced a double number to that of any other tribe, since Manasses was his son, and the tribe of Dan would have produced none. (Ven. Bede)
Salvation to our God; i.e. our salvation is from God, to whom be praise for ever, Amen, benediction, or blessings, thanksgiving. &c. (Witham)
White in the blood of the Lamb. That is, they have been cleansed and purified from sin, by the death, merits, and grace of Christ crucified. (Witham) --- The whole of this verse must be understood in a mystical sense, for we are said to make our garments white in the blood of the Lamb, when we enter into his Church by baptism, or wash away our sins by penance or martyrdom. (Calmet)
Therefore they are before the throne of God....in his temple; i.e. therefore are they now happy in heaven, where the temple was represented to be, as observed before. --- He that sitteth on the throne shall dwell, or dwelleth over them. (Witham)
The Lamb, which is in the midst of the throne, God and man, shall rule  them as a shepherd does his flock. By the Greek, And shall lead them unto fountains of living waters;  literally, to the fountains of life of waters; shall bless them with everlasting happiness. (Witham) --- He represents the happiness of the saints, under the idea of being exempt from all the wants and evils of this life. For we are not able, according to truth itself, to conceive the happiness that is prepared for us; wherefore we must content ourselves with considering what it is not, rather than what it is. He, nevertheless, seems to compare heaven to a temple or palace, in which we observe ministers and servants all in their proper order, his counselors (if we may be allowed the expression) and friends seated in presence of their prince, and the souls of the just singing the praises of the Most High. (Car.)
Reget eos, Greek: poimanei, &c.
Ad vitæ fontes aquarum, Greek: epi zoes pegas udaton; not Greek: zosas, as in some manuscripts.