Romans 2:25

For circumcision indeed profiteth, if thou be a doer of the law: but if thou be a transgressor of the law, thy circumcision is become uncircumcision.

Beginning here, and to the end of the chapter, Paul discussed circumcision, which was to the Jew, and especially to them here addressed, a refuge of last resort, wherein, if all else failed, he still might claim eternal life as his just inheritance. Charles Hodge noted that:

It is obvious that the Jews regarded circumcision as in some way securing their salvation. That they did so regard it may be proved, not only from such passages of the New Testament where the sentiment is implied, but also by the direct assertion of their own writers. Such assertions have been gathered in abundance from their own works by Eisenmenger, Shoettgen, and others. For example, Rabbi Menachem, in his commentary on the Book of Moses (folio 43, column 3), says, "Our Rabbis have said, that no circumcised man will see hell."[18]

Circumcision, as Paul discussed it here, refers to the rite itself, not to the whole law of which that rite was a covenant seal. The fact that Paul began with a declaration that circumcision was profitable for them that kept the law was apparently in anticipation of the advantages pertaining to the Jew which he discussed immediately afterwards in Romans 3. But, while allowing the validity of the rite when used as God intended it, Paul did not hesitate to blast this last refuge of apostates by showing that not even circumcision could do a man any good eternally, if he did not keep the law. To transgressors of the law (not occasional and inadvertent transgressors, but the hardened and impenitent) circumcision became uncircumcision. Every Israelite should have known that already. Historically, circumcision had never been alleged as any reason why the death penalty should not have been executed upon sabbath breakers (Numbers 15:35) and such men as Achan (Joshua 7:24), nor as any impediment to their Rabbi's casting out of their synagogues persons they judged unworthy. From these well-known facts, they should have been able to deduce the great corollary that no such thing as circumcision could possibly prevent the judgment of God upon apostates.