{7} How was it then reckoned? when he was in circumcision, or in uncircumcision? Not in circumcision, but in uncircumcision.

(7) He proves that it belongs to the uncircumcised (for there was no doubt of the circumcised) in this way: Abraham was justified in uncircumcision, therefore this justification belongs also to the uncircumcised. Nay, it does not belong to the circumcised, in respect of the circumcision, much less are the uncircumcised shut out from it because of their uncircumcision.

People's New Testament

4:10 How was it then reckoned? To settle the question, whether this blessedness applies to Gentiles as well as Jews, the inquiry is made whether Abraham was a Jew or Gentile when it was said of him, His faith was counted for righteousness (Ro 4:5). He was not circumcised for at least fourteen years after this statement was made of him. Compare Ge 15:6 with Ge 17:25. He was then justified, without circumcision, while yet a Gentile.

Wesley's Notes

4:10 Not in circumcision - Not after he was circumcised; for he was justified before Ishmael was born, Gen 15:1 - 21; but he was not circumcised till Ishmael was thirteen years old, Gen 17:25.

Matthew Henry's Concise Commentary

4:1-12 To meet the views of the Jews, the apostle first refers to the example of Abraham, in whom the Jews gloried as their most renowned forefather. However exalted in various respects, he had nothing to boast in the presence of God, being saved by grace, through faith, even as others. Without noticing the years which passed before his call, and the failures at times in his obedience, and even in his faith, it was expressly stated in Scripture that he believed God, and it was counted to him for righteousness, Ge 15:6. From this example it is observed, that if any man could work the full measure required by the law, the reward must be reckoned as a debt, which evidently was not the case even of Abraham, seeing faith was reckoned to him for righteousness. When believers are justified by faith, their faith being counted for righteousness, their faith does not justify them as a part, small or great, of their righteousness; but as the appointed means of uniting them to Him who has chosen as the name whereby he shall be called, the Lord our Righteousness. Pardoned people are the only blessed people. It clearly appears from the Scripture, that Abraham was justified several years before his circumcision. It is, therefore, plain that this rite was not necessary in order to justification. It was a sign of the original corruption of human nature. And it was such a sign as was also an outward seal, appointed not only to confirm God's promises to him and to his seed, and their obligation to be the Lord's, but likewise to assure him of his being already a real partaker of the righteousness of faith. Thus Abraham was the spiritual forefather of all believers, who walked after the example of his obedient faith. The seal of the Holy Spirit in our sanctification, making us new creatures, is the inward evidence of the righteousness of faith.