Tertullian — Against Praxeas 13

Here, then, those miscreants provoke questions. And so they say, Baptism is not necessary for them to whom faith is sufficient; for withal, Abraham pleased God by a sacrament of no water, but of faith . But in all cases it is the later things which have a conclusive force, and the subsequent which prevail over the antecedent. Grant that, in days gone by, there was salvation by means of bare faith , before the passion and resurrection of the Lord. But now that faith has been enlarged, and has become a faith which believes in His nativity, passion, and resurrection, there has been an amplification added to the sacrament, viz., the sealing act of baptism ; the clothing, in some sense, of the faith which before was bare, and which cannot exist now without its proper law.

For the law of baptizing has been imposed , and the formula prescribed: Go, He says, teach the nations , baptizing them into the name of the Father , and of the Son , and of the Holy Spirit . The comparison with this law of that definition, Unless a man have been reborn of water and Spirit, he shall not enter into the kingdom of the heavens, has tied faith to the necessity of baptism . Accordingly, all thereafter who became believers used to be baptized . Then it was, too, that Paul , when he believed , was baptized ; and this is the meaning of the precept which the Lord had given him when smitten with the plague of loss of sight , saying, Arise, and enter Damascus; there shall be demonstrated to you what you ought to do, to wit — be baptized , which was the only thing lacking to him.

That point excepted, he had sufficiently learned and believed the Nazarene to be the Lord, the Son of God .