Irenaeus

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 the flesh typified that after the Spirit. For "we," says the apostle, "have been circumcised with the circumcision made without hands." And the prophet declares, "Circumcise the hardness of your heart."