The Immutability or Unchangeability of God is an attribute that "God is unchanging in his character, will, and covenant promises."

God's immutability defines all God's other attributes: God is immutably wise, merciful, good, and gracious: Primarily, God is almighty/omnipotent (all powerful), omnipresent (present everywhere), and omniscient (knows everything); eternally and immutably so. Infiniteness and immutability in God are mutually supportive and imply each other. An infinite and changing God is inconceivable; indeed, it is a contradiction in definition.

The holy Catholic Apostolic Roman Church believes and confesses that there is one true and living God, Creator and Lord of heaven and earth, almighty, eternal, immense, incomprehensible, infinite in intelligence, in will, and in all perfection, who, as being one, sole, absolutely simple and immutable spiritual substance, is to be declared as really and essentially distinct from the world, of supreme beatitude in and from Himself, and ineffably exalted above all things which exist, or are conceivable, except Himself.

It could be said that God knows beforehand all the possible steps each creature – i.e., which steps each human could take at any given moment, whether good or bad, and God also knows beforehand from eternity what he will or will not ultimately do in any given situation, knowing that sometimes he will say he is going to do something worse – and then doing either a less negative response or nothing at all. This allows God to exhibit a unique form of free will, and to show his mercy and forgiveness and holiness – qualities God values.