God is the source of justice. In God there is such an ineffable communion of life, that is, the Father lives in the Son and the Spirit and vice versa to such an extent unimaginable to us. There is a complete giving, between the Father, Son and Holy Spirit, a transcendent perfection of life and love which we call God's holiness. This inner source of justice is beautifully expressed by the angel's song:
Holy, Holy, Holy is the Lord God of angel hosts! (Is 6:3)
With the advent of man upon earth, justice became operative in the lives of mankind because of man's dependence upon God and other men. In justice, each man and woman is to be given what is due to them, and in justice, God is to be given obedience, honor and worship that is due to Him because he is our creator, sustainer and our final end, that is, our loving Father. Mankind at its beginning rebelled against the living God thereby incurring the punishment of death. St. Paul rightly wrote: "All men have sinned and are deprived of the glory of God."(Rm 3:26)
But, how can a limited creature offend God infinitely? "As a deed of a creature sin is indeed finite, but as an insult to the infinite God it is infinite."
God's Justice and Mercy in the Old Covenant
In Exodus we read that the Lord cried out to Moses:
"The LORD, the LORD, is a merciful and gracious God,slow to anger and rich in kindness and fidelity,...forgiving wickedness and crime and sin; yet not declaring the guilty guiltless...." (Ex. 34:6-7)
Thus we see that Justice and Mercy are harmonized. Mercy does not eliminate justice but is the power of love which prevails over sin and infidelity. (John Paul II)
Christ the Justice of God and the Mercy of God
O how sad your death; how infinite your love!
Since man had sinned infinitely, only a divine being who was both God and man could make reparation for this great wrong deserving of eternal death.
So God sent his Only Son, Jesus in his humanity to satisfy God's Justice and at the same reveal his infinite love and readiness to forgive his poor creatures.
With King David we must cry out: " Have mercy on me, O God, in your goodness; in the greatness of your compassion wipe out my offense." (Ps 51:1)
Divine Mercy Devotion