That is an old interpretation your employing, the Catholic interpretation.We are saved by grace through faith and those with faith uphold His law Romans 3:31
Here is the first verse in chapter 3 of Romans.
Romans 3:1
Then what advantage does the Jew have? Or what is the benefit of circumcision?
Who is Paul talking too here?
The Gentiles, certainly not.
The Gentiles are not circumcised, not under the law.
What is the benefit of circumcision?
Start reading the text yourself and stop blindly quoting verses out of context.
Romans 3:31
Do we then nullify the Law through faith? Far from it! On the contrary, we establish the Law.
What is the benefit of circumcision?
Why does Paul establish the law that the Gentiles never knew.