(CG 1/016). That in God there is no Passive Potentiality (Book 1: Of God As He Is In Himself) (Summa Contra Gentiles) (Aquinas, Thomas, St.)

IN every compound there must be actuality and potentiality. For a plurality of things cannot become one thing, unless there be actuality and potentiality. For things that are not one absolutely, are not actually united except by being in a manner tied up together or driven together: in which case the parts thus got together are in potentiality in respect of union; for they combine actually, after having been potentially combinable. But in God there is no potentiality: therefore there is not in Him any composition.

Every compound is potentially soluble in respect of its being compound, although in some cases there may be some other fact that stands in the way of dissolution. But what is soluble is in potentiality not to be, which cannot be said of God, seeing that He is of Himself a necessary Being.