He entered the class of catechumens, and after the usual period of three years of instruction and probation, he was baptized by Meletius in his twenty-third year (369 or 370). From this time on, says Palladius, "he neither swore, nor defamed any one, nor spoke falsely, nor cursed, nor even tolerated facetious jokes." His baptism was, as in the case of St. Augustin, the turning point in his life, an entire renunciation of this world and dedication to the service of Christ. The change was radical and permanent.
Meletius, who foresaw the future greatness of the young lawyer, wished to secure him for the active service of the church, and ordained him to the subordinate office of rector (anagnostes, reader), about A.D.370. The rectors had to read the Scripture lessons in the first part of divine service (the "Missa Catechumenorum"), and to call upon the people to pray, but could not preach nor distribute the sacraments.
The first inclination of Chrysostom after baptism was to adopt the monastic life as the safest mode, according to the prevailing notions of the church in that age, to escape the temptations and corruptions of the world, to cultivate holiness and to secure the salvation of the soul. But the earnest entreaties of his mother prevailed on him to delay the gratification of his desire. He relates the scene with dramatic power. She took him to her chamber, and by the bed where she had given him birth, she adjured him with tears not to forsake her. "My son," she said in substance, "my only comfort in the midst of the miseries of this earthly life is to see thee constantly, and to behold in thy features the faithful image of my beloved husband who is no more. This comfort commenced with your infancy before you could speak. I ask only one favor from you: do not make me a widow a second time; wait at least till I die; perhaps I shall soon leave this world. When you have buried me and joined my ashes with those of your father, nothing will then prevent you from retiring into monastic life. But as long as I breathe, support me by your presence, and do not draw down upon you the wrath of God by bringing such evils upon me who have given you no offense." 
These tender, simple and impressive words suggest many heart-rending scenes caused by the ascetic enthusiasm for separation from the sacred ties of the family. It is honorable to Chrysostom that he yielded to the reasonable wishes of his devoted mother. He remained at home, but turned his home into a monastery. He secluded himself from the world and practiced a rigid asceticism. He ate little and seldom, and only the plainest food, slept on the bare floor and frequently rose to prayer. He kept almost unbroken silence to prevent a relapse into the habit of slander.
His former associates at the bar called him unsociable and morose. But two of his fellow-pupils under Libanius joined him in his ascetic life, Maximus (afterwards bishop of Seleucia), and Theodore of Mopsuestia. They studied the Scriptures under the direction of Diodorus (afterwards bishop of Tarsus), the founder of the Antiochian school of theology, of which Chrysostom and Theodore became the chief ornaments. 
Theodore was warmly attached to a young lady named Hermione, and resolved to marry and to leave the ascetic brotherhood. This gave rise to the earliest treatise of Chrysostom -- namely, an exhortation to Theodore, in two letters.  He plied all his oratorical arts of sad sympathy, tender entreaty, bitter reproach, and terrible warning, to reclaim his friend to what he thought the surest and safest way to heaven. To sin, he says, is human, but to persist in sin is devilish; to fall is not ruinous to the soul, but to remain on the ground is. The appeal had its desired effect; Theodore resumed his monastic life and became afterwards bishop of Mopsuestia in Cilicia and one of the first biblical scholars. The arguments which Chrysostom used, would condemn all who broke their monastic vows. They retain moral force only if we substitute apostasy from faith for apostasy from monasticism, which must be regarded as a temporary and abnormal or exceptional form of Christian life.
 Socrates and Kurtz (in the 10th edition of his Kirchengeschichte, I. 223), confound this Basil with Basil the Great of Cappadocia, who was eighteen years older than Chrysostom and died in 379. Chrysostom's friend was probably (as Baronius and Montfaucon conjecture) identical with Basil, bishop of Raphanea in Syria, near Antioch, who attended the Council of Constantinople in 381. Comp. Stephens, l. c. p. 14; and Venables in Smith & Wace, I. 297.  De Sacerd. I. 5.  Socrates and Sozomenus represent Diodor and Karterius as abbots under whom Chrysostom lived as monk, but Neander (in the 3d ed. I. 29) thinks it more likely that Chrysostom was previously instructed by Diodor at Antioch.  Parænesis ad Theodorum Lapsum, in Migne's ed. I., Pars I. 277-319. The second letter is milder than the first, and was written earlier. It is somewhat doubtful whether the first refers to the same case. Neander (I. 38 sq.) conjectures that the second only is addressed to Theodore.
 De Sacerd. I. 5.
 Socrates and Sozomenus represent Diodor and Karterius as abbots under whom Chrysostom lived as monk, but Neander (in the 3d ed. I. 29) thinks it more likely that Chrysostom was previously instructed by Diodor at Antioch.
 Parænesis ad Theodorum Lapsum, in Migne's ed. I., Pars I. 277-319. The second letter is milder than the first, and was written earlier. It is somewhat doubtful whether the first refers to the same case. Neander (I. 38 sq.) conjectures that the second only is addressed to Theodore.