Romans 4:9-10 — Cometh this blessedness then upon the circumcision only, or upon the uncircumcision also? for we say that faith was reckoned to Abraham for righteousness.
How was it then reckoned? when he was in circumcision, or in uncircumcision? Not in circumcision, but in uncircumcision.
Abraham was imputed righteousness at least 14 years before he was circumcised, so justification isn't just for the circumcised (Genesis 15).