For precisely because God is pure being— the absolute, perfect, unique, and simple being— we cannot give a definition of him. There is no genus to which he belongs as a member, and there are no specific marks of distinction whereby we can distinguish him from other beings in this genus. Even the being he has, so to speak, in common with all creatures does not pertain to him in the same sense as it does to them (univocally), but only analogically and proportionally.

Bavinck, Herman. Reformed Dogmatics : Volume 2 (p. 95). Baker Publishing Group. Kindle Edition.

Subjects and predicates, when referring to natural and composite entities, are not merely distinct as terms in our statements; the distinctions in terms reflect real distinctions in the things themselves about which we speak. The temptation is to think that since our speech generally functions this way with respect to creatures, then it must also work this way when we speak of God. But herein lies the difficulty: a simple God is not composed of parts; thus, His being cannot be directly directly mapped onto any multipart statements we make about Him.

Divine simplicity accordingly insists on an inescapable incapacity and inadequacy in all our God-talk. We can have only complex propositions and thoughts about the simple God. We cannot discover the manner of God’s being by attempting to read it off the surface grammar of our propositions about Him. The shape of our propositional statements is only suited to correspond in a one-to-one manner to multipart and composite beings.

Dolezal, James E.. All That Is in God: Evangelical Theology and the Challenge of Classical Christian Theism . Reformation Heritage Books. Kindle Edition.

While the logic of divine simplicity may be compelling—God is most absolute in existence and so cannot depend upon that which is not God for any actuality of His being—the doctrine carries with it some deeply counterintuitive and, to some, even strange implications. Chiefly, it means that all that is in God is God. There is no distinction in Him between His act of existence and essence, between His substance and attributes, or between His nature and His intrinsic activity. All these things are nothing but God and do not exist in Him as principles or determinations of His being. From this follow some curious implications for our language about God. It means that our ordinary creaturely patterns of speech (e.g., subject + predicate) do not quite fit God in the way that they fit creatures.

Dolezal, James E.. All That Is in God: Evangelical Theology and the Challenge of Classical Christian Theism . Reformation Heritage Books. Kindle Edition.

From Stromateis 5, 12:

“For both is it a difficult task to discover the Father and Maker of this universe; and having found Him, it is impossible to declare Him to all. For this is by no means capable of expression, like the other subjects of instruction,” says the truth-loving Plato. For he that had heard right well that the all-wise Moses, ascending the mount for holy contemplation, to the summit of intellectual objects, necessarily commands that the whole people do not accompany him. And when the Scripture says, “Moses entered into the thick darkness where God was,” this shows to those capable of understanding, that God is invisible and beyond expression by words. And “the darkness”—which is, in truth, the unbelief and ignorance of the multitude—obstructs the gleam of truth…

…

This discourse respecting God is most difficult to handle. For since the first principle of everything is difficult to find out, the absolutely first and oldest principle, which is the cause of all other things being and having been, is difficult to exhibit. For how can that be expressed which is neither genus, nor difference, nor species, nor individual, nor number; nay more, is neither an event, nor that to which an event happens? No one can rightly express Him wholly. For on account of His greatness He is ranked as the All, and is the Father of the universe. Nor are any parts to be predicated of Him. For the One is indivisible; wherefore also it is infinite, not considered with reference to inscrutability, but with reference to its being without dimensions, and not having a limit. And therefore it is without form and name. And if we name it, we do not do so properly, terming it either the One, or the Good, or Mind, or Absolute Being, or Father, or God, or Creator, or Lord. We speak not as supplying His name; but for want, we use good names, in order that the mind may have these as points of support, so as not to err in other respects. For each one by itself does not express God; but all together are indicative of the power of the Omnipotent. For predicates are expressed either from what belongs to things themselves, or from their mutual relation. But none of these are admissible in reference to God. Nor any more is He apprehended by the science of demonstration. For it depends on primary and better known principles. But there is nothing antecedent to the Unbegotten.