"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

Jesus’ words about saying, “Raca,” or “You fool,” are not intended to be a specific detailed list of what we can and cannot say. This instruction is intended to be an illustrative principle to show us:

How close what we say reveals sinful hatred in our hearts.
How something as seemingly inconsequential as name calling is so incredibly serious in the eyes of God.

While the warning about these words instructs us to “mind our words,” more importantly these warnings instruct us to “mind our hearts.” Why? Because as dangerous as our words can be, we are guilty in our hearts long before any words escape our lips.

Once again, because we cannot change our hearts (Jeremiah 17:9-10), we need a Savior who can forgive our sins and change our hearts. His name is Jesus.