This Chapter 5 of Matthew's Gospel purposely echoes Chapter 24 of Exodus. There Moses went up the mountain where God had him gather around him the leaders of the the twelve tribes, before giving Moses the Ten Commandments carved on stone.
There God inaugurated the Old Law, while in today's Gospel Jesus inaugurated the New Law. It was Our Lord's intention that we should build our religious lives around the Beatitudes the way the people of the Old Law built their religious lives around the Ten Commandments.
But something has gone wrong with us. We are still living in the Old Covenant.
We all know the Ten Commandments, and we go to confession when we break any of them. But we ignore Our Lord's request that we be meek and hunger after justice.