In 1 Corinthians 7:39–40 Paul concludes the counsel that he has given to betrothed women. If a man has chosen to marry his betrothed, she is bound to him as long as he lives
(see further Romans 7:1–3).
A widow’s second marriage was often prompted by her need for social and financial protection (especially if she had children in the home). Because of this need, a believing widow could be tempted to accept an unbeliever’s offer of marriage.
For this reason, Paul gives a special exhortation to widows to marry only in the Lord.
In other words, a widow (just like every other church member) may marry only a believer. (As we have seen in 1 Corinthians 7:12–16, a different principle applies when a believer is already married to an unbeliever.)
39 A wife is bound to her husband as long as he lives. But if her husband dies, she is free to be married to whom she wishes, only in the Lord.