A.T. Robertson Commentary 1 Corinthians 7:18

"Was any man called being circumcised? Let him not become uncircumcised. Hath any been called in uncircumcision? Let him not be circumcised." — 1 Corinthians 7:18 (ASV)

Let him not become uncircumcized (μη επισπασθω). Present middle imperative of επισπαω, old verb to draw on. In LXX (I Macc. 1:15) and Josephus (Ant. XII, V. I) in this sense. Here only in N.T. The point is that a Jew is to remain a Jew, a Gentile to be a Gentile. Both stand on an equality in the Christian churches. This freedom about circumcision illustrates the freedom about Gentile mixed marriages.