Answer:
Dante promise he'll tell of their greatness in return.
Step-by-step explanation:
At the beginning of Canto II as Dante is about to cross Hell he realizes that he might not be as worthy as those who have had similar journeys ard returned from them so he invokes the Muses, the ancient goddesses of art and poetry, and promise them to tell about their greatness as he comes back to world of the living, and then he knows about the aid he will receive from Beatriz to make it through hell and be able to come back and keep his word.