Because it was expanded in the new edition so making sure we cover all the important stuff and things that we can remind ourselves of. :) This section will be about Music of the Ainur and Silmarillion proper.
"The cycles begin with a cosmogonical myth: The Music of the Ainur. God and the Valar (or powers: Englished as gods) are revealed. These latter are as we should say angelic powers, whose function is to exercise delegated authority in their spheres (or rule and government, not creation, making or re-making). They are 'divine', that is, were originally 'outside' and existed before the making of the world. Their power and wisdom is derived from their Knowledge of the cosmogonical drama, which they perceived first as a drama (that is as in a fashion we perceive a story composted by someone else), and later as a 'reality'. On the side of mere narrative device, that is, of course meant to provide beings of the same order of beautify, power, and majesty as the 'gods' of higher mythology, which can yet be accepted-- well shall we say baldly, by a mind that believes in the Blessed Trinity.
It moves then swiftly to the History of the Elves, or the Silmarillion proper; to the world as we perceive it, but of course transfigured in a still half-mythical mode: that is it deals with rational incarnate creatures of more or less comparable stature with our own. The Knowledge of the Creation Drama was incomplete: incomplete in each individual 'god', and incomplete if all the knowledge of the pantheon were pooled. For (partly to redress the evil of the rebel Melkor, partly for the completion of all in an ultimate finesse of detail) the Creator had not revealed all. The making, and nature of the Children fo God, were the two chief secrets. All that the gods knew was that they would come, at appointed times. The Children of God are thus primevally related and akin, and primevally different. Since also they are something wholly 'other' to the gods, in the making of which the gods played no part, they are the object of the special desire and love of the gods. These are the First-born, the Elves; and the Followers Men. The doom of the Elves is to be immortal, to love the beauty of the world, to bring it to full flower with their gifts of delicacy and perfection, to last while it lasts, never leaving even when 'slain', but returning--and yet, when the Followers come, to teach them, and the life from which both proceed. The Doom (or the Gift) of Men is mortality, freedom from the circles of the world. Since the point of view of the whole cycle is Elvish, mortality is not explained mythically: it is a mystery of God of which no more is known than that 'what God has purposed for Men is hidden': a grief and an envy to the immortal Elves."
So much to unpack in here and i'm very drawn to what Tolkien thought were the doom of Elves and the Doom of Men and it shows very prominently in the First Age tales and also the Doom of Numenor of what made both races fall. I am also struck by Tolkien saying that the elves love only "delicacy and perfection". First Age elves seem to love high beauty and music more so than Third Age-- but we do see that Third Age elves could be fun and lively as shown by the elves described in The Hobbit...they were not so serious.
Now men of Numenor always envied Elves for their closeness to the gods or Valar and also for their immortality. that is how Sauron had deceived the men of Numenor to go after the Valar in the blessed realm.