John Calvin Commentary Genesis 17:11

"And ye shall be circumcised in the flesh of your foreskin; and it shall be a token of a covenant betwixt me and you." — Genesis 17:11 (ASV)

Ye shall circumcise the flesh of your foreskin—this command would at first sight appear very strange and unaccountable. The subject being discussed is the sacred covenant, in which righteousness, salvation, and happiness are promised, by which the seed of Abraham is distinguished from other nations, so that it might be holy and blessed. And who can say that it is reasonable for the sign of so great a mystery to consist in circumcision? But as it was necessary for Abraham to become a fool in order to prove himself obedient to God, so whoever is wise will both soberly and reverently receive what God seems to us foolishly to have commanded.

And yet we must inquire whether any analogy is apparent here between the visible sign and the thing signified. For the signs which God has appointed to assist our weakness should be adapted to our capacity, or they would be unprofitable. Moreover, it is probable that the Lord commanded circumcision for two reasons: first, to show that whatever is born of man is polluted; then, that salvation would proceed from the blessed seed of Abraham.

Therefore, in the first place, whatever is unique to human beings by natural descent, God condemned in the appointment of circumcision, so that, with the corruption of nature made clear, He might lead them to mortify their flesh. From this it also follows that circumcision was a sign of repentance. Yet, at the same time, the blessing that was promised in the seed of Abraham was thereby marked and attested.

If then it seems absurd to anyone that the token of such an excellent and unique favor was given in that part of the body, let him become ashamed of his own salvation, which flowed from the loins of Abraham. But it has pleased God in this way to confound the wisdom of the world, so that He might more completely abase the pride of the flesh.

And so we now learn, in the second place, how the reconciliation between God and men, which was shown in Christ, was testified to by this sign. For this reason it is called by Paul a seal of the righteousness of faith (Romans 4:11). Let it be sufficient to have briefly touched upon the analogy between the thing signified and the sign.