Outward murder begins with inward anger from a lack of upward worship.
As Jesus builds on the previous paragraph, He shows them how their righteousness should exceed that of the scribes and Pharisees. The scribes and Pharisees knew God’s law better than anyone and gave the impression that they obeyed the law better than anyone. Yet, Jesus did to them what He does to all of us–expose our true motives. Were they obeying to make much of themselves or to make much of God and His Son Jesus? Time would bear out in their treatment of Jesus that they leveraged God’s law and their position to make much of themselves.