For circumcision verily profiteth
The plea from circumcision in favour of the Jews, and their acceptance with God, and justification before him, is here, and in the following verses, considered. The apostle allows that circumcision was profitable; which must be understood whilst it was in force, before the abrogation of it, for since, it is not profitable but pernicious; and then it was only profitable, in case the law was kept:
if thou keepest the law;
that is, perfectly; for circumcision obliged persons to keep the whole law. Now the circumcised Jews did not keep it in such sense; wherefore circumcision was of no use to them, but, on the contrary, was an handwriting against them.
But if thou be a breaker of the law, thy circumcision is made
that is, it is not accounted circumcision; it is of no avail; such a man was all one as an uncircumcised Gentile, and appeared to be uncircumcised in a spiritual sense: the apostle perhaps alludes to a practice among some of the Jews, to bring on and draw over the foreskin, after they had been circumcised; (See Gill on 1 Corinthians 7:18).