What does 1 Corinthians 7:18 mean?

Paul is expanding on the idea that Christians who are married should stay married and Christians who are single should not necessarily seek to get married. He is applying this teaching to many of the areas of a Christian's life.

He begins with circumcision: removing the foreskin from the penis, common especially to the Jewish people (Genesis 17:10–11). Circumcision was required for every male who lived under the law of Moses (Leviticus 12:1–3). Those who come to faith in Christ, however, do not live under the requirements of the law (Romans 6:14).

A primary complaint of the Jewish religious leaders against Paul is exactly what's written in these verses. Not only did he say that new converts to Christianity were not required to be circumcised to be included in God's people, he even forbids them from being circumcised.

This led to understandable tension between Jewish and Gentile Christians living amongst one another. Roman culture often included public baths or competing in the nude in sporting events, as was the custom. In such cases, a person could not very well hide whether they were circumcised. Nor could they avoid the judgments of others, including some Christians, that went along with that awareness.

Should a Jewish person who had been circumcised as an infant seek out surgery to hide or cosmetically reverse his circumcision? Should a Gentile get circumcised, as was required of converts to Judaism, just to be as acceptable to God as possible? In both cases, Paul says "no." Rather, that condition is part of where and how a person was called to Christ. They should stay as they are, in those ways. In the following verses, Paul explains this idea.