How can I give twenty-five statements which cover the content of the book Martin Eden?

I tend to disagree with the treatment of literature by an enumeration of points, especially the requirement of a specific number of them as your question indicates. However, Martin Eden is a complex novel that deserves an in-depth analysis. A key to understanding its themes perhaps can be found by placing it in the context of Jack London's writings as a whole.
London often deals with characters whose identity is conflicted because they are in transition between the "natural" world and the "civilized" world. This conflict applies to his animal protagonists as well as his human ones. In The Call of the Wild Buck is a domesticated dog thrust into the wild world of the Northland; in White Fang it's the opposite journey from the title character's being raised in the wild, forced into a dog-fighting ring, and then rescued and taken to the Southland to live as a domesticated dog. In The Sea Wolf Humphrey is a "gentleman" forced into service on Wolf Larson's very uncivilized ship. Martin Eden is similar to these characters because he begins as a working-class man, a sailor, who transitions to another life as an intellectual, a writer, leaving his old world behind, falling in love with an upper-middle-class girl, Ruth, and attempting to become a part of her world.
Ultimately the transition doesn't work for Martin. He makes enormous sacrifices, educating himself, training himself to become a writer, and saving money by living in cramped conditions where, for instance, he has to hang his bicycle from the ceiling in his tiny apartment. He's met with constant failure for a long time, submitting his work to magazines and being rejected again and again (and even when a piece is accepted he's never paid on time) until finally there is a breakthrough and, against the odds, he becomes a success, a famous writer. In the meantime his courtship of Ruth has failed because he hasn't had the money to make him acceptable to her family, or even to Ruth herself, although she's in love with him. But when "success" finally arrives, to Martin it's an illusion. He has everything he's presumably wanted or needed, money and fame, and now even Ruth offers herself unconditionally to him. But Martin finds that he no longer wants her, or anything else, including returning to his working-class roots. He's a man emptied of will and emotion. He thinks that by removing himself to a new environment, traveling to the South Pacific (which he already is familiar with from his previous life as a sailor) he can jump-start his life and begin anew. But his depression is too deep; he hasn't the will to go forward. On the ship his despair overwhelms him, and he commits suicide by throwing himself overboard.
One does not know if London intended a "moral" or if his story is merely an account of a life in which, when a man strives for something and finally reaches it, he finds it's not what he wanted after all. But what did Martin want? Why did the "transition" from one mode of living to another not work for him, when it did for the characters in London's other books? This question forms the main theme of Martin Eden.