“And now, the plan of mercy could not be brought about except an atonement should be made; therefore God himself atoneth for the sins of the world, to bring about the plan of mercy, to appease the demands of justice, that God might be a perfect, just God, and a merciful God also.” (Alma 42:15)
The Atonement of Jesus Christ brought about the great plan of Justice and Mercy. Mercy is kindness and gentleness. Justice is fairness. God is just and a merciful God. When men sin or do wrong, justice must be applied, satisfied or appeased, put into place or else God would cease to be God. Mercy is also applied in that Jesus suffered for our sins on conditions of our repentance. If we repent, we won’t have to suffer for the punishment, the justice of the law, because Jesus has already paid for our sins. We just need to repent in godly sorrow and not repeat that sin again.