Charles Spurgeon Commentary Romans 4:11

"and he received the sign of circumcision, a seal of the righteousness of the faith which he had while he was in uncircumcision; that he might be the father of all them that believe, though they be in uncircumcision, that righteousness might be reckoned unto them;" — Romans 4:11 (ASV)

That he might be the father of all them that believe, though they be not circumcised: that righteousness might be imputed unto them also:

It is a very remarkable fact. A great many readers of the Book of Genesis would never have noticed it if the Holy Ghost had not called attention to the fact that father Abraham was justified by his faith before he was circumcised; and this is the reason for it – that he might be the father of all believers, whether they are circumcised or uncircumcised. That righteousness might be imputed to them also.