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For it is not written, `Unless a man be born again by the will of his parents’ or `by the faith of those presenting him or ministering to him,’ but, `Unless a man be born again of water and the Holy Spirit.’ The water, therefore, manifesting exteriorly the sacrament of grace, and the Spirit effecting interiorly the benefit of grace, both regenerate in one Christ that man who was generated in Adam”
(Letters 98:2) [A.D. 412]

“Baptism washes away all, absolutely all, our sins, whether of deed, word, or thought, whether sins original or added, whether knowingly or unknowingly contracted”
(Against Two Letters of the Pelagians 3:3:5) [A.D. 420]

“But the sacrament of baptism is undoubtedly the sacrament of regenation: Wherefore, as the man who has never lived cannot die, and he who has never died cannot rise again, so he who has never been born cannot be born again. From which the conclusion arises, that no one who has not been born could possibly have been born again in his father. Born again, however, a man must be, after he has been born; because, ‘Except a man be born again, he cannot see the kingdom of God’ Even an infant, therefore, must be imbued with the sacrament of regeneration, lest without it his would be an unhappy exit out of this life; and this baptism is not administered except for the remission of sins. And so much does Christ show us in this very passage; for when asked, How could such things be? He reminded His questioner of what Moses did when he lifted up the serpent. Inasmuch, then, as infants are by the sacrament of baptism conformed to the death of Christ, it must be admitted that they are also freed from the serpent’s poisonous bite, unless we willfully wander from the rule of the Christian faith. This bite, however, they did not receive in their own actual life, but in him on whom the wound was primarily inflicted.”
(On Forgiveness of Sin, and Baptism, 43:27)

“Moreover, from the time when He said, ‘Except a man be born of water and of the Spirit, he cannot enter into the kingdom of heaven;’ and again, ‘He that loseth his life for my sake shall find it; ‘ no one becomes a member of Christ except it be either by baptism in Christ, or death for Christ.”
(On the Soul and its Origin, 1:10:9)

“One generation and another generation; the generation by which we are made the faithful, and are born again by baptism; the generation by which we shall rise again from the dead, and shall live with the Angels for ever.”
(Augustine – Psalms, 135:11)

s this one Spirit who makes it possible for an infant to be regenerated . . . when that infant is brought to baptism; and it is through this one Spirit that the infant so presented is reborn.