Romans 4:10

πῶς οὖν ἐλογίσθη; To say that his faith was reckoned as righteousness, without mentioning circumcision, suggests that the latter was at least not indispensable; still it is not decisive, and so the further question must be asked, How i.e., under what conditions was his faith thus reckoned to him? Was it when he was circumcised or when he was uncircumcised? History enables Paul to answer, Not when he was circumcised, but when he was uncircumcised. Abraham's justification is narrated in Genesis 15, his circumcision not till Genesis 17, some fourteen years later: hence it was not his circumcision on which he depended for acceptance with God.