There is no commutative justice in God, for no one gives to Him that it should be rendered to him again. There is distributive justice in Him, as the order of the universe shows; for God gives to every creature according to its nature and dignity. Moral virtues which are related to the passions are only ascribed to God metaphorically; for in Him there exists neither sensitive appetite nor passion; but the moral virtues which belong to the works of God are properly attributed to Him, such as justice, magnificence and liberality. The Justice of God is also rightly called Truth, because it constitutes the order in things which agrees with the idea of His Wisdom; for the Intellect of God is their rule and measure.
Above all, we must admit the effects of mercy in God; not after the mode of passion, which has no existence in Him, but as by His own Goodness He removes misery and defect in others.
For God diffuses His perfections in divers ways. When He communicates them absolutely it belongs to goodness; when He apportions them according as they are due to each one it belongs to justice; inasmuch as such perfections are not given for His own benefit, but from gratuitous goodness, it pertains to liberality; while in so far as they supply for all defects it belongs to mercy.
Mercy and Justice are found, indeed, in all the works of God; for the debt which arises from the Divine Justice is twofold; first, that due to God Himself, according to which He does nothing but what befits His Wisdom and Goodness; secondly, that due to the creature, according to which He. disposes all things in suitable proportion.
Mercy is found in all Justice, inasmuch as the debt is reduced somewhat by the Divine Goodness; for Mercy shines forth eminently when more is given than the proportion of things demands; thus in damnation Mercy appears, not by the remission of all punishment, but by the punishment being less than is deserved; while in justification Justice appears, because the fault is remitted on account of Love, which is, itself, mercifully infused.
- text taken from Compendium of the Summa Theologica of Saint Thomas Aquinas, by Bishop Berardus Bongiovanni