The answer
There has never been any conflict between God's justice and His mercy, because there cannot be any contradiction between the qualities of God. God is merciful in His justice and just in His mercy.
The justice of God is full of mercy. The mercy of God is full of justice. We can say that God's justice is a merciful justice and that His mercy is a just mercy. We cannot separate at all God's mercy from His justice.
When we speak on one occasion of justice, and on another of mercy, we are not talking of two different things but of varying aspects of the same thing.
Meimar al-Abd al-Maimluk (a special reading during the Good Friday) imagined a dispute and an argument between God's justice and mercy, which is a kind of theological debate, but it is not correct from the theological point of view, and there have been many objections to it. For naturally such a disagreement never took place. The author of the Meimar, however, wanted to point out the details of the subject in the form of a discussion. This is a style that sometimes makes for interesting reading, but it is not a theologically accurate one.
On the cross, however, as the psalm tells us, justice and mercy join together, or mercy and truth join together (not that they are reconciled!).
The word 'reconciliation' implies the existence of an opposition, and heaven forbid that there should ever be or have been, anything so at odds among the attributes of God!
Even the expression 'join together' means a joining together before us, in our presence, and is conditioned by our concept of this process, while from the theological standpoint, mercy and justice have been joined together in harmony right from eternity. It is as we have said, that God's mercy is full of justice and His justice is full of mercy.
It was on the cross that we saw this union between justice and mercy and it is indeed a permanent union. But we, being human beings, only perceived it when it was brought to our attention on the cross. That was when we saw this beautiful image, which gave to our human minds an understanding that mercy and justice were combined. (
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Thrice-Blessed Pope Shenouda III of Blessed Memory