According to Gilles Emery, Aquinas provides a Trinitarian account of creation. The processions within the being of God are the uncreated exemplars of the acts of creation. Emery (in a contribution to The Theology of Thomas Aquinas ): “In God, procession signified the essential communication of the fullness of divinity: the Father eternally communicates the fullness of divinity to the Son, and together with the Son, he communicates it to the Holy Spirit.”

Thomas distinguishes between relation in created beings and relation in God. From the perspective of creation, procession seems to be the foundation of relation, but Thomas argues that in God relation is absolute, and therefore is identical to the processions. The two terms “procession” and “relation” describe the same divine reality from different angles: “procession refers to the relationship of the divine persons in the manner of an act (to beget, to breathe forth, to be begotten, to be breathed forth), whereas relation signifies this same reality in the manner of a form or a property (paternity of the Father, filiation of the Son, spiration or procession of the Spirit).” To speak of procession is to speak of God “under the dynamic aspect of the eternal communication of the divinity.”

From this he moves to a Trinitarian account of creation. Analogously to the processions of Son and Spirit, Thomas “considers creation under the dynamic aspect of the participation of creatures in being and in the divine perfections. It is on this level of the communication of being , implying the doctrine of analogy, that trinitarian causality is situated. The communication of the entire divine essence of the Trinity is the cause and reason of the communication of creatures, in a radically different order, of a participation in the divine essence: ‘the going-out of the persons in the unity of essence . . . is the cause of the going-out of creatures in the diversity of essence.” As a result creation “finds its foundation in the trinitarian mystery of personal communication or communication of being .”

A few additional thoughts (repeating things I’ve written earlier here): First, Bavinck follows this sort of argument, saying that the whole of creation is pre-contained, eminently, in the Son. He is the “logos” of the creation. Second, what’s pre-contained is not only the objects of creation, but the movement and change of creation. All history is pre-contained in the Son; He is the logos also of history. And that means that the Son is, as it were, the hypostatic form of the decree. Predestination is in Christ because the Father regards the elect with the love He has for His Son; predestination is also in Christ because He is the Word of the Father, and therefore the one who not only personally hypostatizes predestination but the decree in its broadest sense.