light.

Reply Obj. 3: These things are said of God in Scripture
metaphorically. 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.
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SECOND ARTICLE [I. Q. 9, Art. 2]

Whether to Be Immutable Belongs to God Alone?

Objection 1: 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.

Obj. 2: Further, everything in motion moves to some end. What
therefore has already attained its ultimate end, is not in motion. But
some creatures have already attained to their ultimate end; as all the
blessed in heaven. Therefore some creatures are immovable.

Obj. 3: Further, everything which is mutable is variable. But
forms are invariable; for it is said (Sex Princip. i) that "form is
essence consisting of the simple and invariable." Therefore it does
not belong to God alone to be immutable.

_On the contrary,_ Augustine says (De Nat. Boni. i), "God alone is
immutable; and whatever things He has made, being from nothing, are
mutable."

_I answer that,_ God alone is altogether immutable; whereas every
creature is in some way mutable. Be it known therefore that a mutable
thing can be called so in two ways: by a power in itself; and by a
power possessed by another. For all creatures before they existed,
were possible, not by any created power, since no creature is eternal,
but by the divine power alone, inasmuch as God could produce them into
existence. Thus, as the production of a thing into existence depends
on the will of God, so likewise it depends on His will that things
should be preserved; for He does not preserve them otherwise than by
ever giving them existence; hence if He took away His action from
them, all things would be reduced to nothing, as appears from
Augustine (Gen. ad lit. iv, 12). Therefore as it was in the Creator's
power to produce them before they existed in themselves, so likewise
it is in the Creator's power when they exist in themselves to bring
them to nothing. In this way therefore, by the power of
another--namely, of God--they are mutable, inasmuch as they are
producible from nothing