In the combox to my post of earlier today, William Ballow asks and remarks:
If the Divine Essence is imparticiple but the Divine Grace and Life which is the source of salvation is uncreated, is this not implicitly opposed to the definition of divine simplicity supplied by natural theology? Patristic soteriology and Christology unequivocally affirms that humanity is raised to and participates in something truly divine and uncreated which is not the Divine Essence. Only an uncreated power can be the cause or ground of deification, that is certainly a patristic principle.
Although just that topic has been repeatedly debated by both writers and commenters at Pontifications, including yours truly, I have yet to write about it on this blog. Given that this week has been devoted to Orthodox-Catholic discussion here, now seems to me the opportune time to do so.
Jonathan Prejean has already replied in his usual, erudite yet clear way, and I agree with him. But he does not make explicit the main point I want to stress by way of answering Ballow's question. Thus, if we take the term 'divine essence' to mean God as he necessarily is apart from what he does, if follows that the divine essence is incommunicable; for communication would be a complex of "energies," i.e. divine actions, and nothing can communicate that which it is regardless of communication. It also follows that there is a real distinction between the divine essence and the divine "energies," which are God as what he eternally does. (I say "eternally" not "necessarily" in this case because some of God's actions are atemporal and unalterable yet free and thus not necessitated by his essence or nature). But suppose we take the 'divine essence' as Aquinas ordinarily does, to mean God as what he eternally is. Given further Aquinas' doctrine that God is actus purus, and thus has no unrealized potentialities, it follows that there is no real distinction between the divine essence and the divine actions or "energies." And that is also a corollary of his doctrine of divine simplicity (DDS). So the question whether the essence/energies distinction is compatible with DDS depends on what one takes the term 'divine essence' to signify.
The question how we ought to use the term 'divine essence' might seem answerable purely by convention, and indeed that's what it is if we leave matters where I've left them thus far. But of course there remains a problem well known to many readers of this blog.
The most common objection to DDS is that it is logically incompatible with a clear tenet of faith, viz., that God's creating and communicating himself ad extra is free not necessitated. The most satisfactory answer to that objection, I have come to believe, is to affirm that the divine essence as Aquinas uses that term includes a kind of contingency. Thus, what-God-is is eternal and unalterable, but also entails that he do something-or-other he might not have done. Given as much, it was not absolutely necessary that he create at all or that he create this world rather than some other he might have created; that is only conditionally necessary given his free choice to create. But it is necessary that God have done something-or-other ad intra that is free. That God is necessarily and essentially personal (or tri-hypostatic, for those who dislike natural theology) entails that he do some-or-other free action, if only in relation to himself. God is what I call positively mysterious: intelligible, but inexhaustible and hence not fully comprehensible. And the self-contingent God is the same God as the divine essence.