Newness of Spirit

Romans 7:6 "But now we are delivered from the law, that being dead wherein we were held; that we should serve in newness of spirit, and not in the oldness of the letter."

The Sermon on the Mount was revolutionary because it approached God's commandments in a new way. It focused on the spirit of the law, and not merely the letter. Jesus explained what the commandments meant in regard to your heart attitude, not merely outward actions.

Jesus explained that murder isn't just physically killing someone (oldness of the letter). Hating someone in your heart (the newness of the spirit) is the same thing.

Jesus explained that adultery isn't just physically being unfaithful to a spouse (oldness of the letter). Lusting in your heart (the newness of the spirit) is the same thing. 

Your rote physical action of obedience is not what God is after. He wants your heart. And He wants all of it.