Translation
A wife is bound for a period of time that lasts as long as her husband lives; but if the husband should die, she is free to be married to whom she wishes, but only in the LORD.
Paraphrase
A wife is bound to her husband for as long as he lives; but if the husband should die before she does, she is free to be married to whomever she wishes, as long as he is a follower of THE SUPREME RULER.