⇒ This is a literal quote from The Aeneid within Book 6, beginning at lines 126 and continuing with the following:

But to return, and view the cheerful skies,
In this the task and mighty labor lies.

⇒ This is spoken to Aeneas by a prophetess, explaining the requirement of his entering the underworld as a part of his journey to land in Italy – a task which is similar to those seen in the legends of Orpheus, Odysseus, and Heracles.