Cyril of Jerusalem
"Since man is of a twofold nature, composed of body and soul, the purification also is twofold: the corporeal for the corporeal and the incorporeal for the incorporeal. The water cleanses the body, and the Spirit seals the soul. . . . When you go down into the water, then, regard not simply the water, but look for salvation through the power of the Spirit. For without both you cannot attain to perfection. It is not I who says this, but the Lord Jesus Christ, who has the power in this matter. And he says, ‘Unless a man be born again,’ and he adds the words ‘of water and of the Spirit,’ ‘he cannot enter the kingdom of God.’ He that is baptized with water, but is not found worthy of the Spirit, does not receive the grace in perfection. Nor, if a man be virtuous in his deeds, but does not receive the seal by means of the water, shall he enter the kingdom of heaven. A bold saying, but not mine; for it is Jesus who has declared it" (Catechetical Lectures 3:4 [A.D. 350]).
 
Basil the Great
"This then is what it means to be ‘born again of water and Spirit’: Just as our dying is effected in the water [Rom. 6:3; Col. 2:12–13], our living is wrought through the Spirit. In three immersions and an equal number of invocations the great mystery of baptism is completed in such a way that the type of death may be shown figuratively, and that by the handing on of divine knowledge the souls of the baptized may be illuminated. If, therefore, there is any grace in the water, it is not from the nature of water, but from the Spirit’s presence there" (The Holy Spirit 15:35 [A.D. 375]).
 
Ambrose of Milan
"You have read, therefore, that the three witnesses in baptism are one: water, blood, and the Spirit (1 John 5:8): And if you withdraw any one of these, the sacrament of baptism is not valid. For what is the water without the cross of Christ? A common element with no sacramental effect. Nor on the other hand is there any mystery of regeneration without water, for ‘unless a man be born again of water and the Spirit, he cannot enter the kingdom of God’" (The Mysteries 4:20 [A.D. 390]).
 

The Recognitions of Clement
"But you will perhaps say, ‘What does the baptism of water contribute toward the worship of God?’ In the first place, because that which has pleased God is fulfilled. In the second place, because when you are regenerated and born again of water and of God, the frailty of your former birth, which you have through men, is cut off, and so . . . you shall be able to attain salvation; but otherwise it is impossible. For thus has the true prophet [Jesus] testified to us with an oath: ‘Verily, I say to you, that unless a man is born again of water . . . he shall not enter into the kingdom of heaven’" (The Recognitions of Clement 6:9 [A.D. 221]).