New vs. Old vv. 21-48
So, not that Jesus had put pharisaic righteousness into perspective, he proceeded to describe the “new wine” proceeding from both Old Testament Law and Oral Law. He starts with murder and anger.
Murder and Anger vv. 21-26 (Part 1)
You will notice as you read from 5:21 through to the end of the chapter, that each paragraph begins with, “You have heard that it was said…” This, of course, was how the illiterate and unlearned had been taught the law. Both the Old Testament Law and the scribal (Oral) Law were read and/or spoken to the people. Their knowledge was based on hearing. Jesus gives them an “earful” of what lies behind what they have heard.
Of course you should not murder, says Jesus, but that horrific outcome is rooted in something that precedes it: anger. Both epithets, “Raca!” and “You fool!” expose a low view of neighbour. In modern parlance it is utter disdain that spews “Empty head! Blockhead! Numbskull! You stupid! Apostate fool! Outcast! Scoundrel! Foreigner!” These accusations are bathed in contempt and “justify” murder in the view of the murderer. This low life is expendable! The world is better without them! They deserve to die! This outrage fuels the knife. Indeed the thrust of the weapon requires the impetus that anger provides.
Those who heard these words, like us who read them, pause. We’re all guilty of anger. It may not have overcome us yet, but the potential is there to lash out at someone. So Jesus calls for pre-emptive action.