Most preachers like to tell and most congregations like to hear the Gospel in terms of God's love or man's needs. But the Catechism does not begin with what man feels or needs. Rather, it begins with what God requires. Notice, the Catechism here starts with God and not with man. To become right with God, justice must be satisfied.
Justice means giving a person what is their due.
If a customer get newspapers from a papergirl, the customer has to pay his bill. The papergirl has it coming. If a citizen breaks a law, the citizen will have to pay his debt to society by paying a fine, for instance, or by going to jail. He has it coming. It is his due.