Summary: Abraham justified before circumcision
Romans 4 (quickview) : 9Does this blessedness then come upon the circumcised only, or upon the uncircumcised also? For we say that faith was accounted to Abraham for righteousness. 10How then was it accounted? While he was circumcised, or uncircumcised? Not while circumcised, but while uncircumcised. 11And he received the sign of circumcision, a seal of the righteousness of the faith which he had while still uncircumcised, that he might be the father of all those who believe, though they are uncircumcised, that righteousness might be imputed to them also, 12and the father of circumcision to those who not only are of the circumcision, but who also walk in the steps of the faith which our father Abraham had while still uncircumcised.”
Paul now is bringing the argument to a close with the conclusion that Abraham then is in fact the father of both the uncircumcised and the circumcised. The reality is that Abraham is the father of all true believers who place their faith in Yeshua Hamasriach. There is only one important question, the Jew, Paul says must not rely on circumcision but must follow in the footsteps of Abraham and on the journey of faith. This conclusion has some extradionary features. The order in which it is sated suggests that Abraham is in the first place the father of believing Gentiles, since he believed and had the credit of righteousness before he was circumcised and then became the father of believing Jews as well once he was circumcised. Paul is not an advocate of the notion that Abraham can become the father of Gentiles only if they become proselytes, follow the Law and presumably are also circumcised. Paul has already whence argued in chapters 3 and will reiterate in 9:6-13 that the true Jew, the one who is really the descendant of Abraham is one who has faith in that way follows Abraham.
Circumcision is merely the sign from whence we can understand. Righteousness comes through faith because in Genesis 17:11 (quickview)  it is used as a sign yet in Jubilees 15:16 that Gentiles lack the sign on his body that he belongs to the Lord. Paul is using deliberately, the message of a seal here to say something further or a bit different than just a sign. Paul uses “Seal” (sphragis) of a “confirmation” (1 Cor 9;2). Abraham is not used to keep people bondaged to the Law for Abraham knew his obligation to keep the Law in order to be righteous, for Paul then he refers back to his faith and his righteousness through faith. Circumcision then is a confirming of a preexisting condition which can be seen by the clear presentation of Paul’s argument.
The issue becomes more important when we understand in light of Galatians what Paul is implying here. Circumcision is an issue connected to Abraham’s story when it does not appear that the issues are the same as they are in Rome as they were in Galatia, where there were Judaizers? The Judaizer wished to keep the Gentiles bound by the intent of the Law which was to lead one to freedom in Christ, which is why Paul so strongly rebukes Peter for encouraging this line of teaching would have lead to prevision of the Gospel truth which was presented to Peter in Acts 10 (quickview)  in relation to the Gospel for the Gentiles, then later affirmed by the Apostles at the Council of Jerusalem.