Why is The Odyssey by Homer a classic?

It is a classic because after all this time, regardless that the people who first heard it lived 2500 years ago, the story speaks directly to the human condition. The entertaining and exciting adventures, the underlying angst of not getting home, and the story of perserverance against long odds defy the two and a half millenia to be relevant today. When a story gets that kind of staying power, it becomes a member of the family of what we lump together as classics.