(Tolkien on Divine Presence, part 1)
For Tolkien as much as for St. Thomas, then, God is most immanent to his creatures, even closer, as Augustine would say, to creatures than they are to themselves. Not surprisingly, given this common emphasis, Tolkien shares with Thomas something of his concern to distinguish at the same time the divine intimacy with creation from any form of pantheistic heterodoxy. Thomas, for example, opens his discussion of the being of God in things in the Summa with the clarification that “God is in all things; not, indeed, as part of their essence, nor as an accident, but as an agent is present to that upon which it works. For an agent must be joined to that wherein it acts immediately, and touch it by its power; hence it is proved in the Physics that the thing moved and the mover must be together” (ST 1.8.1). Although things participate in God for their being, creatures are not at all on that account “made out of” or composed of God’s own substance. God is in things, instead, not as the material but as the efficient cause of their being (ST 1.44.1-2). Wherever things exist, God is there, on site, not as the raw resource of their being, but as the agent or effecting cause of their existence.
Working within the same Platonic logic of participation as St. Thomas, we find in Tolkien, too, a similar concern to differentiate unambiguously the Platonic participation of things in God for their reality from the pantheistic identification of things with God’s own reality. In his commentary on the Athrabeth, for example, Tolkien describes the Elvish “basic belief” in Eru in these words: he is the “One God Creator, who made (or more strictly designed) the World, but is not Himself the World” (MR 330). In the Athrabeth itself, moreover, Andreth acknowledges, despite her doubts, that Eru is the “One, alone without peer,” who “made Eä, and is beyond it,” yet is nevertheless “already in it, as well as outside,” a statement Finrod further clarifies by adding, in good, scholastic fashion, that “indeed the ‘in-dwelling’ and the ‘out-living’ are not in the same mode” (321-2). Andreth, comprehending Finrod’s meaning, responds by saying: “Truly… So may Eru in that mode be present in Eä that proceeded from Him.” In his commentary on the Athrabeth, Tolkien offers his fullest explanation of the subject, wherein he introduces the metaphor of divine-authorship noted previously: Eru “must as Author always remain ‘outside’ the Drama, even though that Drama depends on His design and His will for its beginning and continuance, in every detail and moment” (335). And again, in the passage cited earlier explaining the Flame Imperishable, Tolkien writes: “It refers rather to the mystery of ‘authorship’, by which the author, while remaining ‘outside’ and independent of his work, also ‘indwells’ in it, on its derivate plane, below that of his own being, as the source and guarantee of its being” (345). For Tolkien, in summary, Eru is indeed “inside” creation, not in the sense that creation is made out of God, which, contrary to Tolkien’s express claim, would effectively raise it to the same “plane” of being as himself, but in the sense that an author is “inside” his story. As author, he is immediately present to and causative of the being of every creature, while his own being is identifiable with the being of none of them.
 “Deus est in omnibus rebus, non quidem sicut pars essentiae, vel sicut accidens, sed sicut agens adest ei in quod agit. Oportet enim omne agens coniungi ei in quod immediate agit, et sua virtute illud contingere: unde in VII Physic. probatur quod motum et movens oportet esse simul.”