The more directly Tolkien’s angelic beings are involved in the affairs of Men and Elves, the more they seem to be attached to their bodies, so much so that they are susceptible to real fatigue and even to a sort of “death,” as is Gandalf’s fate in The Lord of the Rings (L 201). As Tolkien explains the implications of angelic embodiment, “[b]y ‘incarnate’ I mean they were embodied in physical bodies capable of pain, and weariness, and of afflicting the spirit with physical fear, and of being ‘killed’, though supported by the angelic spirit they might endure long, and only show slowly the wearing of care and labour” (L 202). In The Silmarillion, it is further told how the Maiar Melian, after falling in love with the Elf-lord Thingol, became so “bound by the chain and trammels of the flesh of Arda” that she bore him a daughter, Lúthien Tinúviel. At the same time, Melian’s greater association with the physical world also meant for her a greater “power over the substance of Arda” (S 234). The individual Valar who goes the furthest down the path of incarnating himself in the world is Melkor, whose attachment to physical matter is so complete as to make it “permanent,” a fact that makes his later removal from the world nothing less than a form of death or “execution” (MR 394-5 and 399-40). Tolkien’s conception of the Valar’s sub-creative power, therefore, is not simple and static, but complex and dynamic: the more they invest themselves into the material shaping and making of the world, the more power or influence they wield over it, and yet the less power they retain in and for themselves, and thus the more like the conventional, governing angels theorized about by St. Thomas they become. Thus, describing the state of the Valar in later days, Tolkien writes that they “are as we should say angelic powers, whose function is to exercise delegated authority in their spheres (of rule and government, not creation, making, or re-making)” (L 146, emphasis original), and elsewhere Tolkien writes: “The Valar ‘fade’ and become more impotent, precisely in proportion as the shape and constitution of things becomes more defined and settled” (MR 401). As Tolkien continues in the same place:
The longer the Past, the more nearly defined the Future, and the less room for important change (untrammeled action, on a physical plane, that is not destructive in purpose). The Past, once ‘achieved’, has become part of the ‘Music in being’. Only Eru may or can alter the ‘Music’…. The Valar were like architects working with a plan ‘passed’ by the Government. They became less and less important (structurally!) as the plan was more and more nearly achieved. Even in the First Age we see them after uncounted ages of work near the end of their time of work—not wisdom or counsel. (The wiser they became the less power they had to do anything—save by counsel). (MR 401-5)
Here we see a further dimension of the sacrifice involved in the Valar’s choice to enter the world and shape it and govern it for its own good. Perhaps the clearest expression of Tolkien’s view of the sub-creational task in sacrificial terms appears in the Valar Yavanna’s statement that “[e]ven for those who are mightiest under Ilúvatar there is some work that they may accomplish once, and once only” (S 78).
In this Tolkien’s imagination would appear to be governed by yet another Thomistic metaphysical principle, which is that the more organization, actuality, determination, or form a given matter receives, the less potentiality there remains in it to become actualized in other ways (on this, see Pasnau and Shields, The Philosophy of Aquinas, 157). Like the Elves who over the course of Middle-earth’s history must fade and so make way for the age of Men, so Tolkien’s demiurgic Valar, who initially are equivalent to the gods of pagan mythology, likewise fade into the conventional angels familiar in and to the Christian era.