Albert Barnes Commentary Luke 16:18

"Every one that putteth away his wife, and marrieth another, committeth adultery: and he that marrieth one that is put away from a husband committeth adultery." — Luke 16:18 (ASV)

See Barnes on Matthew 5:32.

These verses occur in Matthew in a different order, and it is not improbable that they were spoken by our Saviour at different times. The design, here, seems to be to reprove the Pharisees for not observing the law of Moses, notwithstanding their great pretensions to external righteousness, and to show them that they had really departed from the law.