“The wife is bound by the law as long as her husband liveth; but if her husband be dead, she is at liberty to be married to whom she will; only in the Lord.”
King James Version (KJV)
7:39 Only in the Lord - That is, only if Christians marry Christians: a standing direction, and one of the utmost importance.
1Co 7:39 The wife is bound by the law, etc. One point remains to be discussed, viz., The remarriage of widows. I suppose that the letter of inquiry asked about this. She is at liberty to be married to whom she will. In case of her husband's death, she is free from the marriage bond, and can marry whom she will, with one limitation--she must marry only in the Lord; that is, a Christian. An alien marriage is prohibited. Indeed, so far was an ancient Christian from marrying an unbeliever that the question actually arose whether, when the sinner was converted, he could still live with an unconverted partner. See 1Co 7:12-14.