The pursuit of immortality drives much of the conflict in The Fall. The narrator is admittedly in love with himself, and the thought of his own death torments him. He finds himself struggling to deal with a set of paradoxical facts, including: men will never take you seriously until you’re dead, but once you’re dead, you can’t stick around to enjoy it. According to the narrator, death is a great way to make your point, but it’s likely that men will misinterpret the reasons of your martyrdom, meaning you have died in vain. The narrator seeks moments of immortality in a variety ways (i.e., sex and alcohol). Moments of debauchery, he claims, are the moments when you are most freed from your own mortality.
All of Jean-Baptiste’s actions are driven by the fear of death. Every other "motive" is simply the result of this fear.