In the Odyssey by Homer, the main idea would be a life's journey that is filled with obstacles. Odysseus has been at war for ten years and now he has spent ten years trying to get home. The journey has been long and full of trials, tribulations and obstacles.
The main message of the epic poem Song of Roland is fairly simple: good will always triumph over evil. In this poem, "good" is represented through both honor and justice and always prevails. In the main message, honor as a quality of goodness is quite important. The honor of simply being a "Christian" is stressed.