For judgment is without mercy to the one who has shown no mercy. Mercy triumphs over judgment. (James 2:13)
St Isaac the Syrian further explains the difference between mercy and judgment:
Mercy is opposed to justice. Justice is equality on the even scale, for it gives to each as he deserves. . . . Mercy, on the other hand, is a sorrow and pity stirred up by goodness . . .; it does not requite a man who is deserving of evil, and to him who is deserving of good gives a double portion. If, therefore, it is evident that mercy belongs to the portion of righteousness, then justice belongs to the portion of wickedness. As grass and fire cannot coexist in one place, so justice and mercy cannot abide in one soul. (THE SPIRITUAL WORLD OF ISAAC THE SYRIAN, p 41)