What significance is in the old man's dreams?

The lions symbolize youth, strength, happiness, and hope for the old man.

Santiago's dream about the lions is first described in the opening fifteen pages of the book. He used to see the lions playing on the beaches of Africa, where he grew up, and he remembers that "they played like young cats in the dusk and he loved them". In the midst of his epic battle with the big fish, Santiago again dreams about the lions, and "he (is) happy".