Thomas Aquinas

“ It seems that to be immutable does not belong to God alone. For the Philosopher says (Metaph. ii) that "matter is in everything which is moved." But, according to some, certain created substances, as angels and souls, have not matter. Therefore to be immutable does not belong to God alone. ”

“ Now in the celestial bodies matter is not consistent with privation of form, because the form perfects the whole potentiality of the matter; therefore these bodies are not mutable as to substantial being, but only as to locality, because the subject is consistent with privation of this or that place. On the other hand incorporeal substances, being subsistent forms which, although with respect to their own existence are as potentiality to act, are not consistent with the privation of this act; forasmuch as existence is consequent upon form, and nothing corrupts except it lose its form. ”

“ For as the sun is said to enter a house, or to go out, according as its rays reach the house, so God is said to approach to us, or to recede from us, when we receive the influx of His goodness, or decline from Him. ”

“ Now if the mutability of a thing be considered according to its power for being, in that way all creatures are not mutable, but those only in which what is potential in them is consistent with non-being. Hence, in the inferior bodies there is mutability both as regards substantial being, inasmuch as their matter can exist with privation of their substantial form, and also as regards their accidental being, supposing the subject to coexist with privation of accident ”

“ Thus in every creature there is a potentiality to change either as regards substantial being as in the case of things corruptible; or as regards locality only, as in the case of the celestial bodies; or as regards the order to their end, and the application of their powers to divers objects, as in the case with the angels; and universally all creatures generally are mutable by the power of the Creator, in Whose power is their existence and non-existence. Hence since God is in none of these ways mutable, it belongs to Him alone to be altogether immutable. ”

“ Therefore because God understands and loves Himself, in that respect they said that God moves Himself, not, however, as movement and change belong to a thing existing in potentiality, as we now speak of change and movement.
Reply to Objection 2: Wisdom is called mobile by way of similitude, according as it diffuses its likeness even to the outermost of things; for nothing can exist which does not proceed from the divine wisdom by way of some kind of imitation, as from the first effective and formal principle; as also works of art proceed from the wisdom of the artist. ”

“ It seems that God is not altogether immutable. For whatever moves itself is in some way mutable. But, as Augustine says (Gen. ad lit viii, 20) , "The Creator Spirit moves Himself neither by time, nor by place." Therefore God is in some way mutable. ”

“ First, because it was shown above that there is some first being, whom we call God; and that this first being must be pure act, without the admixture of any potentiality, for the reason that, absolutely, potentiality is posterior to act. Now everything which is in any way changed, is in some way in potentiality. Hence it is evident that it is impossible for God to be in any way changeable. Secondly, because everything which is moved, remains as it was in part, and passes away in part; as what is moved from whiteness to blackness, remains the same as to substance ”

“ Augustine there speaks in a similar way to Plato, who said that the first mover moves Himself; calling every operation a movement, even as the acts of understanding, and willing, and loving, are called movements. ”