In defense of divine impassibility against the avalanche of criticism and rejection within conservative Reformed and evangelical circles, Michael Horton proposes that it could be beneficial to shift the discussion of divine passions to the persons of the Trinity, rather than God's essence. (Charles J. Rennie, "A Theology of the Doctrine of Divine Impassibility: (I) Impassibility and the Essence and Attributes of God," in Richard S Baines, Richard C. Barcellos et al, eds., Confessing the Impassible God, 285)
This particular proposal, though well-intended, provides more confusion than clarification. As argued above, Horton is correct to insist upon the distinction between the human essence and a particular human person ... His attempt to posit similarly of God, however, is incoherent, since God is his essence and the essence if not "shared" in a generic sense, but is numerically and indivisibly one. The persons of the Trinity not only each have the whole undivided divine essence, but they have no subsistence outside of or apart from the divine essence. The divine essence is not a fourth "thing" that the divine persons "share." The divine essence is undivided and common to all three persons of the Trinity. (Rennie, "Attributes," in Baines et al, 286)
I have always suspected that there is an over-fixation on ontology in many areas of theology and philosophy, and here is one more example that seems to validate my suspicion. In fact, interactions like this make all the crazy misrepresentation during the EFS debacle more understandable, since it seems that those who hold to "classical theism" are incapable of thinking of anything but being, being and being.
Dr. Horton in his systematic theology, when he is trying to shift the discussion of passion from the essence to the persons of the Godhead, is operating under a personalist ontology and epistemology, or what he calls "covenant ontology" and "covenant epistemology." One of the books in our reading lists in his Christian Mind class at Westminster California, essentially the prolegomena course, was a book by Ester Meek entitled Longing to Know, which is Meek's retooling of Michael Polanyi's philosophy towards a more Christian context. In my opinion, the Polanyi-Meek reworking of epistemology is deeply flawed, but I do agree with it on one issue - the desire to get away from traditional philosophical categories of being and knowing. Operating under a personalist or covenant ontology, Horton shifts the discussion of passions to the dynamism of the persons of the Trinity, thus preserving impassibility of the Godhead while having the persons being able to be emotionally involved.
Whatever one thinks of this proposal, we must note that there is indeed a shift away from a traditional focus on ontology. The differentiation of the persons of the Godhead of course start with the nature of God as being both one and three. But the persons of the Godhead are also in action, or dynamic. Thus, before creation, God covenants with God in the Pactum Salutis. Thus, God hears our prayers and interacts with us. Thus, God speaks and continue to speak through His Word the Scriptures. In other words, the persons of the Godhead have a "being" or nature, but they are also in act. The ad intra relations of the Godhead are there, but there is also the ad extra works of the persons of the Godhead. In God ad extra, we can and should say that God interacts with His Creation, and expression of emotions is one such interaction.
When Charles Rennie therefore writes that "The persons of the Trinity not only each have the whole undivided divine essence, but they have no subsistence outside of or apart from the divine essence," he is the one in confusion, for it is clear enough from Horton's writings that he is precisely not dwelling on ontology, neither of the essence or of the persons. Of course, for orthodoxy, we should all agree that for the persons, "there is no subsistence outside of or part from the divine essence" and that "the divine essence is not a fourth 'thing' that the divine persons 'share.'" But one can hold those orthodox truths and still believe in Horton's proposal, because Rennie totally is confused over Horton's proposal. This confusion is because of the incessant focus it seems on being, being and being.
Look, I get it that the doctrine of impassibility is denied and attacked in many quarters. But retreating back to 17th century theology and philosophy isn't going to do anything except hurt your cause, and those of us who are interested in truth and apologetics instead of intellectual retreat and beating drums aren't going to join you there.