As in most adventure stories, the theme is perseverance, continuing on the journey despite hardships, despite doubt, despite even reason. When there is every indication that the journey will be difficult, you keep on going, because the outcome is worth the struggle. If before you even begin, common sense tells you this will be fruitless, you keep on going.
Axel serves as the voice of “reason” in this story. He argues with Professor Lidenbrock that the message discovered in the old book cannot be true. But he is swayed by his uncle and reluctantly agrees. When he finally sees that his uncle’s faith in the message is justified, he becomes more enthusiastic. Despite danger and even being separated from the others, he does not give up.
Professor Lidenbrock is excited by the thought of discovery. He makes his plan and follows it, ever willing to adjust his strategy with new discoveries.
Hans is the picture of duty. He has no discoveries to make, only a job to do, and he does it well. He does not show emotion about what he sees. It is just what it is. He perseveres because that is what he is required to do. Otherwise, he has no vested interest in the journey.
In all three, their perseverance guides them along the way. As a result, they gain knowledge and especially wisdom.