Romans 4:11-12

And he received circumcision as a sign, a seal of the righteousness that he had by faith while he was still uncircumcised. So then, he is the father of all who believe but have not been circumcised, in order that righteousness might be credited to them. And he is then also the father of the circumcised who not only are circumcised but who also follow in the footsteps of the faith that our father Abraham had before he was circumcised.

(v11-12, NIV)

If righteousness was attained through circumcision, all would need to be circumcised to be declared righteous. However, Abraham was justified before circumcision, so that he would be the father of the circumcised and the uncircumcised. Even if there are those who are circumcised, it is not by their circumcision but by their faith. They may follow in Abraham's example in circumcision if they so choose, but it is more importantly his example of faith that is to be followed.