Adam Clarke on Romans 2:25

For circumcision verily profiteth - It is a blessing to belong to the Church of God and wear the sign of the covenant, provided the terms of the covenant are complied with.

But if thou be a breaker of the law - If thou do not observe the conditions of the covenant, the outward sign is both without meaning and without effect. This was a maxim of the rabbins themselves; for they allowed that an apostate or ungodly Israelite must go to hell, notwithstanding his circumcision.