What would be a central idea in "life on the mississippi " by mark twain?

Mark Twain writes about the Mississippi and gives it personified feautures. It is the most important character in the story. Although the river is not a person, it functions as a character throughout the story. The central idea is this idea that the Mississippi is so great, it deserved to be a character. This shows the importance of the Mississippi in Twain's life.