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 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.
This poem, written by Bilbo Baggins, refers to Aragorn Elessar, son of Arathorn, and the High King of the reunited kingdoms of Gondor and Arnor. It is sometimes called The Song of the Dunadan. It was written before Aragorn's ascension to the throne, before the War of the Ring even began. Each line is prophetic...
All that is gold does not glitter,
This line refers to Aragorn's perfect lineage. Descended from Isildur in an unbroken line of first children over 39 generations, Aragorn is the rightful heir to the kingdoms of Elendil the Tall. The only surviving heir of Númenor, he is also the High King of Men and the Heir of the House of Elros Tar-Minyatur, son of Eärendil the Blessed.
Not all those who wander are lost;
During the years before the War of the Ring, Aragorn wandered far and wide over the lands of Middle-Earth. In the North he was called Strider, and was the leader of the Rangers of that land. His "wanderings" during those years led him to become the powerful leader and king during and after the War.
The old that is strong does not wither,
Aragorn had a remarkable lifespan, between three and four times the age of normal men. This line lets us know that his age was to his benefit rather than detriment in forging him into the man he became.
Deep roots are not reached by frost.
When Gandalf came to Middle-Earth, Círdan commended to him Narya, the Red Ring of Fire, saying that with it he might be able to "rekindle the valour of old in a world that grows chill." This line shows clearly that the darkening of Middle-Earth did not affect the power or faith of Aragorn Elessar.
From the ashes a fire shall be woken,
This sentence figuratively speaks of Aragorn's rise from the near-destruction of the house of Isildur to become the king of the reunited kingdoms. It also refers to this name of his sword, Andúril, the Flame of the West, formerly Narsil the blade of Elendil.
A light from the shadows shall spring;
The most powerfully prophetic of all the lines, this tells of the arrival of Aragorn to the fields of Pelennor. Coming out of the darkness of the Paths of the Dead, Aragorn arrived in the glory of the Sea-Kings of old to win the victory there.
Renewed shall be blade that was broken,
Aragorn's sword Andúril was forged from the shards of Narsil, the broken blade of Elendil the Tall, which cut the Ring from the hand of Sauron at the end of the Second Age. It was reforged in Imladris just after the Council of Elrond and its fire was rekindled in the War of the Ring.
The crownless again shall be king.
Since the death of the last king of Gondor at the hands of the Morgul-lord, the Crown of Gondor lay in the Hall of Kings in Minas Tirith. Unlike the Scepter of Annúminas, which was committed to Elrond, the Crown lay without a keeper. Thus the crownless is both Aragorn and the whole house of Elendil and Elros his ancestor, restored to their kingship by Aragorn.
How did a simple hobbit write such a powerful verse, you ask? Perhaps he had the help of elves ... or a wizard?
Sources
J.R.R. Tolkien.
The Lord of the Rings.
New York: Houghton Mifflin, 2001.