The word essence comes to mind, and I think it's a useful synonym of the words spirit or soul.
I remember watching a movie once where the guy who plays George Costanza on Seinfeld--don't remember his real name--plays a man who kills a Canadian boy in a hit-and-run in a low-budget film. All kinds of extradition crap complicates bringing him to trial, which eventually happens. Because of how all the laws worked, he got off on technicality.
The boy's father who spoke at the trial appealed that the man be found guilty based on the "spirit" of the law, rather than the letter of the law.
That's what comes to mind when I think of spirit or soul: essence, or "the point of [it]", "it" being to whatever you apply it.