Such power in ages long ago Could Indra’s gracious boon bestow. O, hear the Vánars’ voices, hear The shouting which proclaims them near. E’en now about to cross they seem Sweet Gomatí’s delightful stream.

In plain words: Hanuman says this power comes from an old blessing given by Indra, king of the gods. He tells Bharat to listen to the shouts of the monkeys. They are about to cross the Gomati river.