In Tolkien's legendarium, Men and Elves are the same 'species', but the fate of their spirits are very different.
Men die and their spirits leave the world, and go... nobody knows where.
But Elves - whether they live on Middle Earth and fade, are killed and return to the realm of spirits, or live in the undying lands - are bound to the fate of the world. This means that Elves die when the world ends; and, what happens to their spirits is not known.
Therefore, both Men and Elves need faith in the goodness of The One, or God - who is the creator - if they are not to despair.
Although Men's spirits leave the world, they need faith that the spirits are not simply annihilated at that point; and that whatever fate God has in store for them, it must ultimately be for their Good.
Likewise Elves must have faith that when, eventually, the world comes to an end, their spirits will not likewise utterly perish; but that God will instead have some good fate for them in whatever unknown situation comes after the end of the world.
From Men's perspective, the Elves will not have to worry about what happens for a long time - many lives of Men; so Man's need for faith is much more urgent if he is not to succumb to despair.
Elves seem to love the world, get fulfillment from life, more than Men; and so can remain interested by things for longer. But sooner or later their motivation fades - and they begin to focus on the futility of merely existing while waiting for the end of the world. The threat of despair is therefore something that creeps-up on elves, slowly but inexorably.
In the end, when confronted by the future, Elves and Men share the same ultimate, existential, need for hope based upon faith in the goodness of God. Neither have any other 'guarantee' - since neither race can look beyond their own - apparent - annihilation; and they have no dependable 'information' on what will happen afterwards.
Tolkien himself regarded this situation as having been changed for Men with the incarnation of Jesus Christ (in an era after the legendarium), and the resultant new information ('revelation') that there would be a life beyond death: resurrection.
How this putatively affected Elves was only hinted at by Tolkien - with the idea that Elves might not be resurrected, but perhaps rejuvenated in Men's Heaven - having been (I infer, Tolkien did not use the word) translated to Heaven (i.e. earth remade, creation cleansed of the evil taint introduced by Melkor/ Morgoth) in something like the way Roman Catholics envisage for the Blessed Virgin Mary.
This was perhaps conceivable for Tolkien; because - although prone to sin - Elves had not undergone a theological Fall in the same way as Men.
I find a lesson for Modern Man in all this.
Modern Men no longer believe the revelations about Jesus Christ - they do not believe the Bible, the teachings of the church, and have rejected tradition to the point of regarding it as evil.
Modern men have, therefore - pretty much - returned to something like the situation of Tolkien's Men. We have no knowledge of God or resurrection - but only the possibility of 'mere' Hope; a Hope based upon sheer and un-evidenced Faith in the ultimate Goodness and care of God.
Such a Faith in such a God, can only have its roots in personal assurance, deriving from a situation of a pure act of direct inner-confrontation with reality; and the insight, intuition, sense of sure knowing which may arise in such a situation.
Such a faith in God can provide a basis for Hope - but that Hope must be non-specific (much like that of Tolkien's Elves and Men) unless it has, in addition, more explicit knowledge of the work of Jesus Christ and the possibility of resurrection.
This is why the Holy Ghost is such a vital aspect of Christian belief; since the assumption is that the ascended Christ provided this new source of explicit knowledge, unavailable to the 'ancient' Men (and Elves) envisaged by Tolkien.
The Holy Ghost can - it is asserted - provide those who seek His guidance with specific information about the future of Men beyond Death (i.e. resurrection into Heaven); and guidance on how to partake in that future.
This information is available to us; but was not available to Tolkien's Men; yet the ability to avail ourselves of this knowledge is dependent-upon our prior Faith and Hope in the goodness of God, the creator - for us, as for the Men (and Elves) of Tolkien's world.