"You have heard that it was said to those of old, 'You shall not murder,’ and whoever murders will be in danger of the judgment.' But I say to you that whoever is angry with his brother without a cause shall be in danger of the judgment. And whoever says to his brother, 'Raca!' shall be in danger of the council. But whoever says, 'You fool!' shall be in danger of hell fire.”
Matthew 5:21-22

What is the connection between murder and sinful anger?

First, all anger is not sinful. God gets angry and God cannot sin. Our anger is frequently sinful because it is not righteous anger. The difference between sinful anger and righteous anger is that:

Sinful anger is selfishly motivated. It is about ME. It is motivated by my pride.
Righteous anger is on behalf of God or someone else who is being violated or treated unrighteously. It is motivated by a love for God’s glory.
Sinful anger desires vengeance.
Righteous anger desires justice, knowing that vengeance belongs only to the Lord! (I pray we all know the difference!)
Sinful anger is almost always merely emotional.
Righteous anger is more cerebral and spiritual.

Sinful anger is connected to murder, while righteous anger is not.

Second, the connection between sinful anger and murder is that sinful anger both begin in the heart. Murder begins in the heart and is acted out. Anger likewise begins in the heart, is often proclaimed with the mouth, and may even be acted out physically—but stops short of taking another person’s life.

Since God judges the heart and not merely the outward manifestations (or lack thereof), Jesus is saying that before God, angry and murderous hearts (and every shade of gray in between), are equally damnable.

As I have said for years, “All sins are equally damning (before God), but not all sins are equally damaging (in practice).” We’ll unpack that concept a little more next time.