Many readers will no doubt recall this fascinating passage in The Silmarillion (20) which draws an equivalency between the life of the Valar and the life of Arda. I have always wanted more of an explanation than we find here.
Thus it came to pass that of the Ainur some abode still with Ilúvatar beyond the confines of the World; but others, and among them many of the greatest and most fair, took the leave of Ilúvatar and descended into it. But this condition Ilúvatar made, or it is the necessity of their love, that their power should thenceforward be contained and bounded in the World, to be within it for ever, until it is complete, so that they are its life and it is theirs. And therefore they are named the Valar, the Powers of the World.
A comment in the recently published The Nature of Middle-earth (2021: 14) presents an even more interesting comment along similar lines, suggesting a likeness (parallel? analogy?) between the spirits and bodies of Incarnates and between the Valar and Arda itself:
The Valar having entered Arda, and being therein confined within its life, must also suffer (while therein and being as it were its spirit, as the fëa is to the hröa of the Incarnate) its slow ageing.
I am sure there's more to think about and say here, and I want to take a look at the other versions of the Ainulindalë. For now, though, I just wanted to toss the two passages into the cauldron and let them simmer.
