Is it a sin for a divorced couple to have sex even if there was no adultery? —S.K.
Yes, since they are no longer married (by definition). Good question, though. Divorce requires grounds. Adultery is one of several grounds, though not the only one. If a divorce is groundless, it is sinful. The marriage is still dissolved (as I understand the Scriptures to say), but contrary to the will of God.
Your question may imply that in the absence of adultery, all divorces are invalid—or that somehow the couple are still somehow married. If so, this train of thought rests on a misunderstanding. Please read my piece on Instone-Brewer; I hope that will clarify.
