To say that God is simple is to express God’s transcendence. All divine persons, because of the identity of supposit and nature are simple. However, Aquinas accepts the predication of persona composita, composed person, of the Son Incarnate. Does that mean that God and Christ Incarnate are opposed as the transcendent and the immanent God? No, and if one is tempted to conclude to such an opposition, one has a wrong understanding of divine transcendence and of divine simplicity. To predicate simplicity of God is to say that there is no one else who qualifies for being God than God himself. For simplicity says that divine being and divine essence or nature are identical, and thus no one else shares in divine essence and no one else shares in divine being. This makes ‘simple’ to be a predicate different from all other predicates, since it does not describe a certain feature of God’s divine nature, but it says something about all of our language about God: we cannot but employ predicates in talking about God, thus suggesting that God participates in something essential bigger than God alone, but this suggestion should be denied; we cannot but employ predicates in talking about God, thus suggesting that God has a certain being, but this suggestion should be denied. The language we use is fit for talking about creatures. This language uses words that are defined. Each definition contains something that is common and something that is different. The definition of human being for example employs ‘animal’, a genus, and ‘rationalis’ a specific difference, combining together to form the definition of the species human being. Any proposition about something concrete, using words with a certain definition, intensifies this difference between something common, the predicate, and something particular, the subject. The distinctions used reflect the very structure of human thinking and human speaking, which expresses that something is unique by its being different from other things. This will not do for God, since God does not differ from the world in this sense. God is not transcendent in the sense that he needs a difference to be the unique one he is. God is not different within a certain genus, on the basis of a common similarity. This is what simplicity expresses: God is ‘outside’ of any genus, and thus God is not different from creatures the way in which creatures mutually differ. God differs differently. This is where description of God’s being or nature stops, and where we discover that simplicity and transcendence are actually words qualifying our thinking and speaking about God, instead of qualifying God himself. All of our language about God should be analyzed in such away, as the analysis of words and propositions used analogously in fact does, to account for this unique uniqueness of God.
Such an account undermines the opposition between transcendence and immanence, because God is not transcendent in such a way that he is simply ‘outside of or ‘above’ the world, and thus not transcendent in such a way that it would exclude his ‘descent’ into the world. The true light that came into the world was already in the world (Jn 1). A proper understanding of divine transcendence does not exclude divine immanence; formulated in terms of ‘union’, God was already united to the world before he was united with this human nature. However one interprets divine simplicity, an understanding that implies God to be unknowable and ineffable because God is simply ‘outside of or ‘above’ creation is utterly misleading.
Henk J. M. Schoot, Christ the Name of God, pp. 144-145