It's a common feature in epic poetry where the poet calls upon a muse, god, or other higher power for inspiration and aid in telling the story.
Some famous examples of invocations include:
* Homer's *The Iliad*: "Sing, goddess, of the wrath of Achilles, son of Peleus"
* Virgil's *The Aeneid*: "Arms and the man I sing, who first from shores of Troy..."
* Milton's *Paradise Lost*: "Sing, Heavenly Muse, that on the secret top..."
The invocation serves multiple purposes:
* Establishes the epic's grand scope and importance.
* Invokes divine favor for the poet's work.
* Sets the tone and theme of the poem.
* Provides a sense of awe and reverence for the story being told.