William Burkitt on 1 Corinthians 7:18

Here the apostle proceeds to exhort the Corinthians to be content with the lot and condition which God had distributed unto them, and to frame themselves to walk Christianly in it.

Particularly he shows, That if any person amongst them were a native Jew, and so circumcised, and afterwards converted to Christianity, he should neither trouble himself to get off that mark from his flesh, nor affect the state of him who, being a Gentile, had never been circumcised.

On the other side, if any of them were native Gentiles, and never circumcised, but now converted to Christianity, let him not affect the state of one who was a native Jew, and circumcised: For circumcision is nothing and uncircumcision is nothing; that is, nothing now available to salvation, nothing that renders persons more or less acceptable in the sight of God; but the keeping of the commandments of God, this is all in all. For God regards not men's outward conditions, but obedience to his commands.

Christianity consists not in a warm zeal, either for or against outward ceremonies, but in positive holiness, and a strict conformity to divine precepts.