In Romans 4:11, what was circumcision a seal of for Abraham?

Romans 4:11 states that circumcision was a seal of the righteousness of the faith Abraham had while he was yet uncircumcised. It confirmed the righteousness he received by believing God before circumcision was instituted, demonstrating that justification comes by faith apart from circumcision.

Les explains that Abraham received the sign of circumcision as a seal of the righteousness of the faith he had while still uncircumcised. For the first 2,000 years there was no hint of circumcision or the Mosaic Law. Abraham came out of Ur of the Chaldees, an Assyrian by birth and a non-Jew, while in idolatry, and by faith he left before circumcision was implemented. Thus he became the father of all who believe, including the uncircumcised, so that righteousness might be imputed to them also. Les ties Abraham to us, showing that we are not part of the circumcision covenant and are uncircumcised in Scriptural relationships.

Romans 4:11

And he received the sign of circumcision, a seal of the righteousness of the faith which he had yet being uncircumcised: that he might be the father of all them that believe, though they be not circumcised; that righteousness might be imputed unto them also:

Was Abraham justified before circumcision was ever mentioned?

Abraham was justified by faith while still uncircumcised, before circumcision had even been mentioned to him. Scripture states he received circumcision later as a sign and seal of the righteousness of the faith he already possessed. His justification therefore did not come by virtue of circumcision or the covenant relationship.