Romans 2:25

Circumcision has value if you observe the law, but if you break the law, you have become as though you had not been circumcised.

(v25, NIV)

Paul is still addressing the Jews. These Jews boasted in the law, and they also boasted in their circumcision. This mark they wore with pride. However, what Paul says here seems to slap their circumcision in the face. Paul has just been talking about hypocrisy and he alludes to the fact that these Jews he is addressing are hypocrites. In some way shape or form, whether open or secret, they break the law. As a result, their breaking of the law in a way undoes their circumcision. Breaking the law renders you as one who is uncircumcised. The thing they boasted in they really can't boast in because they are as if they are uncircumcised.

Paul doesn't say here that circumcision is of no value. He most definitely starts off this paragraph saying that circumcision has value. However, it has value if you observe the law. Now, the point here is not that everyone should go and physically circumcise themselves. However, there is a sort of undoing of this physical mark the Jews boasted in that occurs when you break the law.