Tolkien wrote this famous, hopeful poem during the dark days of WWII when Great Britain was under attack. It is found twice in The Fellowship of the Ring (first volume in The Lord of the Rings trilogy). In the book, Bilbo wrote the poem so that Frodo may one day understand Strider's true identity as Aragorn.
As I think of what was going on in the world when Tolkien was writing these books, the poem becomes even more meaningful. The reassurance he offers, the message of hope, and an unconquerable positive attitude in the face of difficulty become even more amplified.
Even though the poem is meant to identify and confirm Aragorn's identity, I also love the poem for its universal message of hope, and the important reminder that there is a divine spark within us all, which can always be rekindled through the saving atonement of our "King of kings".
All that is gold does not glitter,
Not all those who wander are lost;
The old that is strong does not wither,
Deep roots are not reached by the frost.
From the ashes a fire shall be woken,
A light from the shadows shall spring;
Renewed shall be blade that was broken,
The crownless again shall be king."
~J.R.R. Tolkien, The Lord of the Rings