This is important to illustrate that Jesus is proclaiming a New Law that does not destroy the old Law but fulfills it. The New Law is not about revenge and getting square. The New Law is about love. Jesus legislates for loving our enemies. All of the Commandments are in the Beatitudes, and very much more.
Let us look at the last verse. You must therefore be perfect as your heavenly Father is perfect. This is a big clue to the Sermon on the Mount. To be as perfect as the heavenly Father is surely an impossibility. To be poor in spirit, pure in heart, love the enemy are likewise impossible dreams for any of us. We will always be short of that. But the Law of the New Covenant is that we should aim for that. We are promised the Holy Spirit's help. We will be canonised for trying.
You can keep the Ten Commandments by will power on a good day! You can never live the Beatitudes without the grace of God!! You will live them fully in heaven.