Jesus allows only one valid reason for a man to divorce: if his wife has been unfaithful (see Matthew 5:32). For those who thought divorce was easy, Jesus emphasizes God's created order. Marriage is meant to last forever (see Mark 10:11–12).
commits adultery: This refers to a man who divorces his wife without a valid reason. If he remarries, it is the same as adultery. Jesus aims to reestablish that marriage is permanent.