Quaeritur: How are Trinitarian Processions Compatible with Divine Immutability and Eternity?

Quaeritur: How are Trinitarian Processions Compatible with Divine Immutability and Eternity?

Quaeritur: In Summa theologiae Ia, q.27, Aquinas explains in great detail what is going on inside the Trinity. The two internal processions: the Father generates the Son. The Father and the Son spirate the Holy Spirit. All of these terms seem to imply movement—emanating from, coming forth, a breathing out, etc., yet we learned earlier that God is immutable. There is no movement in God as that would imply potentiality, and in God there is no potential, He is pure act. How can movement and immutability seemingly coexist?

There also seems to be an ordering or succession of the divine persons—God the Father, the First Principle, unbegotten. God the Son, begotten, generated from God the Father. God the Holy Spirit, spirated from God the Father and God the Son. But in God there is one divine essence, not shared by the three persons, but subsisting in each one. And in God essence and existence are one and the same thing. How can we reconcile the one essence and existence of the divine persons with their apparent succession?

Respondeo: Excellent questions.  God is indeed immutable Pure Act, and therefore in Him there cannot be any sort of motion whatsoever.  It is also not quite correct to say that there is "succession" in God, because that would imply motion.  Rather, the Divine Processions are eternal processions: the Father eternally begets the Son, and the Father and Son eternally spirate the Holy Ghost.  The consequence is a priority and posteriority among the persons in God: but not a temporal priority, since the Father does not exist "before" the Son, nor do they exist "before" the Holy Ghost.  Rather, there is an order among the persons with regard to their procession.  The Father proceeds from no one: He is innascible, unbegotten, unspirated.  The Son proceeds from the Father by way of generation, and together with the Father (the Father through Him) spirates the Holy Ghost.

Moreover, none of this brings division into the Divine Simplicity, because these processions are all identical to the Divine Essence.  St. Thomas, in an objection, argues thus:

Obj. 2: "Everything which proceeds differs from that whence it proceeds. But in God there is no diversity; but supreme simplicity. Therefore in God there is no procession."  

To this, he responds: 

Ad 2: "Whatever proceeds by way of outward procession is necessarily distinct from the source whence it proceeds, whereas, whatever proceeds within by an intelligible procession is not necessarily distinct; indeed, the more perfectly it proceeds, the more closely it is one with the source whence it proceeds. For it is clear that the more a thing is understood, the more closely is the intellectual conception joined and united to the intelligent agent; since the intellect by the very act of understanding is made one with the object understood. Thus, as the divine intelligence is the very supreme perfection of God (Question [14], Article [2]), the divine Word is of necessity perfectly one with the source whence He proceeds, without any kind of diversity." (ST Ia, q. 27, a. 1, ob. 2, ad 2).