"Our God is one," etc.

Reply Obj. 2: "One" which is the principle of number is not
predicated of God, but only of material things. For "one" the
principle of number belongs to the genus of mathematics, which are
material in being, and abstracted from matter only in idea. But "one"
which is convertible with being is a metaphysical entity and does not
depend on matter in its being. And although in God there is no
privation, still, according to the mode of our apprehension, He is
known to us by way only of privation and remotion. Thus there is no
reason why a certain kind of privation should not be predicated of
God; for instance, that He is incorporeal and infinite; and in the
same way it is said of God that He is one.
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FOURTH ARTICLE [I, Q. 11, Art. 4]

Whether God Is Supremely One?

Objection 1: It seems that God is not supremely _one._ For "one" is so
called from the privation of division. But privation cannot be greater
or less. Therefore God is not more "one" than other things which are
called "one."

Obj. 2: Further, nothing seems to be more indivisible than what
is actually and potentially indivisible; such as a point and unity.
But a thing is said to be more "one" according as it is indivisible.
Therefore God is not more _one_ than unity is _one_ and a point is
_one._

Obj. 3: Further, what is essentially good is supremely good.
Therefore what is essentially _one_ is supremely _one._ But every
being is essentially _one,_ as the Philosopher says (Metaph. iv).
Therefore every being is supremely _one;_ and therefore God is not
_one_ more than any other being is _one._

_On the contrary,_ Bernard says (De Consid. v): "Among all things called
one, the unity of the Divine Trinity holds the first place."

_I answer that,_ Since _one_ is an undivided being, if anything is
supremely _one_ it must be supremely being, and supremely undivided.
Now both of these belong to God. For He is supremely being, inasmuch
as His being is not determined by any nature to which it is adjoined;
since He is being itself, subsistent, absolutely undetermined. But He
is supremely undivided inasmuch as He is divided neither actually nor
potentially, by any mode of division; since He is altogether simple,
as was shown above (Q. 3, A. 7). Hence it is manifest that God is
_one_ in the supreme degree.

Reply Obj. 1: Although privation considered in itself is not
susceptive of more or less, still according as its