Justice is a word we hear every day. We use it in personal relationships, in social conventions, with respect to legislation, and to the verdicts rendered in court. As commonplace as the word is, it has perplexed philosophers who seek an adequate definition of it.
Sometimes we link or equate justice with what is earned or deserved. We speak of people getting their just deserts in terms of rewards or punishments. But rewards are not always based upon merit. Suppose we hold a beauty contest and declare that a prize will be awarded to the person deemed most beautiful. If the "beauty" wins the prize, it is not because there is something meritorious in being beautiful. Rather, justice is served when the most beautiful contestant is rightfully awarded the prize. If the judges vote for someone they do not deem the most beautiful (for political reasons or because they are bribed) then the outcome of the contest will be unjust.
For reasons such as the above, Aristotle defined justice as "giving a person what is his or her due." What is "due" may be determined by ethical obligation or by some prior agreement. If a person is punished more severely than his crime deserves, the punishment is unjust. If a person receives a lesser reward than she has earned, then the reward is not just.
How then does mercy relate to justice? Mercy and justice are obviously different things, though they are sometimes confused. Mercy occurs when wrongdoers are given less punishment than deserved or greater rewards than they earned.
God tempers His justice with mercy. His grace is essentially a kind of mercy. God is gracious to us when He withholds the punishment we deserve and when He rewards our obedience despite the fact that we owe obedience to Him, and so we do not merit any reward. Mercy is always voluntary with God. He is never obligated to be merciful. He reserves the right to exercise His grace according to the good pleasure of His will. For He says to Moses, "I will have mercy on whomever I will have mercy, and I will have compassion on whomever I will have compassion" (Romans 9:15).
People often complain that because God does not distribute His grace or mercy equally on all people, He is therefore not fair. We complain that if God pardons one person He is therefore obligated to pardon everybody.
Yet, we see clearly in Scripture that God does not treat everyone equally. He revealed Himself to Abraham in a way He did not to other pagans in the ancient world. He graciously appeared to Paul in a way He did not appear to Judas Iscariot.
Paul received grace from God; Judas Iscariot received justice. Mercy and grace are forms of nonjustice, but they are not acts of injustice. If Judas's punishment was more severe than he deserved, then he would have something about which to complain. Paul received grace, but this does not require that Judas also receive grace. If grace is required from God, if God is obligated to be gracious, then we are no longer speaking of grace, but of justice.
Biblically, justice is defined in terms of righteousness. When God is just, He is doing what is right. Abraham asked God a rhetorical question that can only have one obvious answer: "Shall not the Judge of all the earth do right?" (Genesis 18:25). Likewise, the apostle Paul raised a similar rhetorical question: "What shall we say then? Is there unrighteousness with God? Certainly not!" (Romans 9:14).