Light
In this text, light is used as a symbol for creation. On the one hand, this represents divine creation, including the creation of the world and living creatures. Alternatively, it could represent the creativity of an author such as Tolkien, when creating a literary universe.
The Creation of Middle Earth
The creation of Middle Earth could be seen as an allegory for the divine creation of the Earth by God. Tolkien himself was a Catholic, and strong religious themes underly his writing.
Mythology
The idea of mythology is a key motif in this text. Tolkien intended this to be a collection of mythological stories about Middle Earth, providing a historical backdrop to the Lord of the Rings trilogy.
The Corruption of Creation
The rise of Melkon and his evil ambitions might be an allegory for the corruption of perfect divine creation. Before Melkon's transgression, the world was in a state and harmony and peace, which may be an allusion to the biblical "fall of man."
Darkness
Darkness in this text represents the tragic, dreadful events that occur in this fictional universe. For example, the narrator describes how "among the tales of sorrow and of ruin that came down to us from the darkness of those days."