“Till death do us part” or “As long as we both shall live” is a sacred covenant promise-the same kind Jesus made with his bride when he died for her.
Therefore, what makes divorce and remarriage so horrific in God’s eyes is not merely that it involves covenant-breaking to the spouse, but that it involves misrepresenting Christ and his covenant.
Christ will never leave his wife. Ever. There may be times of painful distance and tragic backsliding on our part. But Christ keeps his covenant forever. Marriage is a display of that!
That is the ultimate thing we can say about it. It puts the glory of God’s covenant-keeping love on display.”
John Piper, This Momentary Marriage: A Parable of Permanence