Batman’s crusade against crime is motivated by his ongoing commitment to strive to keep the unkeepable promise that defines him. This commitment gives his life a meaning that isn’t connected to his own personal satisfaction. In fact, it’s connected to his own personal sacrifice. Batman’s promise binds him to Gotham for however long she may need him.*
*William Irwin, Mark D. White, Robert Arp. Batman and Philospophy: The Dark Knight of the Soul/Batman’s Promise. (2008), p99.