Matthew 5:20-48 shows Jesus intensifying the Law (anger=murder, lust=adultery) to reveal how far short everyone falls

In the antitheses of Matthew 5 ("you have heard... but I say to you"), Jesus does not lower the Law's standard—he reveals its true heart-level requirement, which is even harder than the letter. Anger is as serious as murder; lust is adultery in the heart. Jesus also addresses divorce, oaths, retaliation, and love of enemies. The purpose is to expose human inability to meet God's standard—setting up the need for a Savior.