In Matthew 5:48 Jesus says, “You therefore must be perfect, as your heavenly Father is perfect”; Our Father is perfectly and completely holy, he wants his children to pursue holiness in order that they may be more and more like him. Jesus gives this command as a conclusion to everything he said previously to it. If we look at the context that this command comes from we see that Jesus has a practical and specific ideas in mind as to what “being perfect” looks like.
The first topic that Jesus addresses is in verses 21-26 is anger. Jesus states,
“You have heard that it was said to those of old, ‘You shall not murder; and whoever murders will be liable to judgment.’ But I say to you that everyone who is angry with his brother will be liable to judgment; whoever insults his brother will be liable to the council; and whoever says, ‘You fool!’ will be liable to the hell of fire. So if you are offering your gift at the altar and there remember that your brother has something against you, leave your gift there before the altar and go. First be reconciled to your brother, and then come and offer your gift. Come to terms quickly with your accuser while you are going with him to court, lest your accuser hand you over to the judge, and the judge to the guard, and you be put in prison. Truly, I say to you, you will never get out until you have paid the last penny.”
Jesus here addresses sinful anger and forgiveness (reconciliation). The original command concerning murder is expanded by Christ to encompass not just the action, but the intention behind the action. Anger is an emotion and, by itself, is not sinful. But when anger is not properly handled it can become sinful. The proper response to anger is reconciliatory forgiveness. Not just a forgiveness that gives mental ascent to release another person from obligation, but forgiveness that actually brings the two persons involved into better relationship with each other.
Because of Christ’s substitutionary atonement for us on the cross, our perfect Father can never again be angry toward his children for their sin. No matter what we have done, no matter what we do, and no matter what we will do, through Christ, our perfect Father has given more than a mental ascent to release us from our obligation to pay for our sin, he made Christ pay for them on our behalf that we might enter into a better and more perfect relationship with him.