Romans 4:11

For albeit it is subsequently that he is called "a father of many nations," still it is of those (nations) who, as the fruit of the "faith" which precedes digamy, had to be accounted "sons of Abraham."

Paul taught us both that Abraham received circumcision as a sign and that while he was still uncircumcised he gave evidence of righteousness arising from faith.

See you how he shows the Jews to be as it were of the class of parasites (i.e. guests), rather than those in uncircumcision, and that these were added to the others? For if he was justified and crowned while in uncircumcision, the Jews came in afterwards, Abraham is then the father first of the uncircumcised, which through faith appertain to him, and then of those in the circumcision. For he is a forefather of two lines. See you faith lightening up? for till it came the patriarch was not justified. See you the uncircumcision offering no hindrance? for he was uncircumcised, yet was not hindered from being justified. The circumcision therefore is behind the faith. And why wonder that it is behind the faith, when it is even behind the uncircumcision. Nor is it behind faith only, but very far inferior to it, even so far as the sign is to the reality of which it is the sign; for instance, as the seal is to the soldier. And why, he says, did he want a seal then? He did not want it himself. For what purpose then did he receive it? With a view to his being the father alike of them that believe in uncircumcision and in circumcision. But not of those in circumcision absolutely: wherefore he goes on to say, "To them who are not of the circumcision only." For if to the uncircumcised, it is not in that he is uncircumcised that he is their father, although justified in uncircumcision; but in that they imitated his faith; much less is it owing to circumcision that he is the forefather of those in the state of circumcision, unless faith also be added.

But how are we children of faith? and of whose faith, if not Abraham's?

He resolves a naturally arising objection. Someone might perhaps object: if Abraham was justified before circumcision, then why was he circumcised? The Apostle answers: he "received the sign of circumcision" — in place of a seal, confirming that he was justified by faith, which he …

Having shown that the blessing of forgiveness of sins is obtained not only in circumcision but also in uncircumcision on the ground that Abraham was justified when he was still uncircumcised, the Apostle now responds to an objection. For someone could say: if Abraham was …

After Abraham's justification by faith had continued several years only a grant by parole, for the confirmation of Abraham's faith God was pleased to appoint a sealing ordinance, and Abraham received it; though it was a bloody ordinance, yet he submitted to it, and even received it as a special favour, the sign of circumcision, &c.

The gospel way of justification is by an imputed righteousness, mellei logizesthai -- it shall be imputed; he uses a future verb, to signify the continuation of this mercy in the church, that as it is the same now so it will be while God has a church in the world, and there are any of the children of men to be justified; for there is a fountain opened that is inexhaustible.

And - After he was justified. He received the sign of circumcision - Circumcision, which was a sign or token of his being in covenant with God. A seal - An assurance on God's part, that he accounted him righteous, upon his believing, before he was circumcised.

And he received the sign of circumcision,....

And he received the sign of circumcision, a seal, etc. - So far was obedience to the law of circumcision from being the reason of his justification, that he not only received this justification before he was circumcised, but he received the sign of circumcision, as a seal of the pardon which he had before actually received. And thus he became the father, the great head and representative, of all them that believe; particularly the Gentiles, who are now in precisely the same state in which Abraham was when he received the mercy of God. Hence it appears, says Dr. Taylor, that the covenant established with Abraham, Gen 17:2-15, is the same with that, Gen 12:2, Gen 12:3; Gen 15:5, etc.; for circumcision was not a seal of any new grant, but of the justification and promise which Abraham had received before he was circumcised; and that justification and promise included the Gospel covenant in which we are now interested. St. Paul refers to this, Gal 3:8: The Scripture foreseeing that God would justify us, heathens, through faith, preached before the Gospel unto Abraham, saying, In thee shall all nations be blessed. The whole of the apostle’s argument, in this fourth chapter to the Romans, proves that we, believing Gentiles, are the seed of Abraham, to whom, as well as to himself, the promise was made; and that the promise made to him is the same in effect as that promise which is now made to us; consequently, it is the Abrahamic covenant in which we now stand; and any argument taken from the nature of that covenant, and applied to ourselves, must be good and valid. It is also undeniably evident, from this eleventh verse, as well as from Gen 17:1-11, that circumcision was a seal or sign of the Gospel covenant in which we now stand. […]