Genesis 17:9

1. Moreover, we learn from the Scripture itself, that God gave circumcision, not as the completer of righteousness, but as a sign, that the race of Abraham might continue recognisable. For it declares: “God said unto Abraham, Every male among you shall be circumcised; and ye shall circumcise the flesh of your foreskins, as a token of the covenant between Me and you.” This same does Ezekiel the prophet say with regard to the Sabbaths: “Also I gave them My Sabbaths, to be a sign between Me and them, that they might know that I am the Lord, that sanctify them.” And in Exodus, God says to Moses: “And ye shall observe My Sabbaths; for it shall be a sign between Me and you for your generations.” These things, then, were given for a sign; but the signs were not unsymbolical, that is, neither unmeaning nor to no purpose, inasmuch as they were given by a wise Artist; but the circumcision after th …

6. The next verse too is suspicious, "If ye believed Moses, ye would also believe me;" for the religion of Moses is so entirely different from that of Christ, that if the Jews believed one, they could not believe the other. Moses strictly forbids any work to be done on Sabbath, and gives as a reason for this prohibition that God made the world and all that is therein in six days, and rested on the seventh day, which is Sabbath; and therefore blessed or sanctified it as His haven of repose after toil, and commanded that breaking the Sabbath should be punished with death. The Jews, in obedience to Moses, insisted strongly on this, and so would not even listen to Christ when He told them that God always works, and that no day is appointed for the intermission of His pure and unwearied energy, and that accordingly He Himself had to work incessantly even on Sabbath. …

3. To return to what I said of your not accepting everything in the Old Testament. You do not admit carnal circumcision, though that is what is written; nor resting from all occupation on the Sabbath, though that is enjoined; and instead of propitiating God, as Moses recommends, by offerings and sacrifices, you cast these things aside as utterly out of keeping with Christian worship, and as having nothing at all to recommend them. In some cases, however, you make a division, and while you accept one part, you reject the other. Thus, in the Passover, which is also the annual feast of the Old Testament, while it is written that in this observance you must slay a lamb to be eaten in the evening, and that you must abstain from leaven for seven days, and be content with unleavened bread and bitter herbs, you accept the feast, but pay no attention to the rules for its observance. …

Chapter 24. 32. And if any one seek for divine authority in this matter, though what is held by the whole Church, and that not as instituted by Councils, but as a matter of invariable custom, is rightly held to have been handed down by apostolical authority, still we can form a true conjecture of the value of the sacrament of baptism in the case of infants, from the parallel of circumcision, which was received by God’s earlier people, and before receiving which Abraham was justified, as Cornelius also was enriched with the gift of the Holy Spirit before he was baptized. …