How did Abraham come into faith if it was not through a covenant relationship?
Abraham came into faith while still in Ur of the Chaldees, in idolatry, before circumcision or any covenant relationship. God spoke to him there and told him to leave for a place He would show him, and by faith Abraham left. He received righteousness before circumcision was ever mentioned.
Les explains that Abraham did not come into this faith by virtue of his covenant relationship. God dealt with him when he was still in Ur of the Chaldees, in the midst of idolatry, and told him to leave and go to a place God would show him. By faith Abraham left, not after circumcision was implemented, but before. Verse 11 says he received the sign of circumcision as a seal of the righteousness of the faith he had while yet uncircumcised. So he came into this justification position before circumcision had even been mentioned to him. This ties Abraham to all who believe, including the uncircumcised, that righteousness might be imputed unto them also.