A friend of mine once wrote the following incredibly profound comment in a discussion of Love, Justice and Mercy:
There is no law of justice.
This is a misnomer that does not appear in the text of scriptures anywhere. There are rights of mercy and demands of justice. God must respect the demands of justice or He would cease to be God. The rights of mercy must be claimed by one who can exercise them to overpower justice.
So, the real questions are:
a) Who demands justice?
b) Who claims mercy?
c) How does mercy overpower but not rob justice?
The answers to those questions are written throughout the scriptures and even more plainly in the writings of Joseph Smith.
a) Satan, the accuser of his brethren (Revelations) and each of us when we refuse to forgive those who've offended us and when we refuse to forgive ourselves
b) Christ (Moroni 7:27)
c) Consider the account of the woman taken in adultery. A sinless intermediary pleads for mercy on behalf of the guilty. Because this intermediary willingly bore the infinite and eternal anguish of injustice for us, we who have a right to demand justice are shamed by His gracious and merciful forgiveness into laying down our own stones. We refuse to accuse our brethren and the breach between us is healed through the pure love of Christ. We are reconciled to each other and it changes our nature such that we can become reconciled to God. This is why only the merciful can receive mercy.
Joseph Smith taught that "if we do not accuse each other, God will not accuse [us]" and that "if a man has no accusers he will enter heaven".
All of this becomes clear when you remember that God is primarily the great parent of the universe. Would your children continue to honor you, respect you, and love you if you treated them with favoritism and injustice? You would cease to have an uncompelled dominion (d&c121) - they would not choose to follow after you. You must respect their need for justice. If one comes to you with a complaint against another, you must address it fairly.
Now imagine that your oldest child willingly accepts the punishment for your second child every time that second child misbehaves. The second child comes to you with a complaint against the third child. Your oldest comes between the two younger children and implores the second child, for whom he has willingly and selflessly suffered, to forgive the younger child. Your second child, seeing that his older brother loves the youngest child also, and feeling the love his older brother has shown him already, albeit undeserved, relinquishes his right to just recompense in favor of saving the youngest child.
Justice can't be robbed. It must be willingly abdicated.