I guess just to be in control of things? But then you take a step back and realize absolutely all of his plan is utterly moronic. Then you take a step back further and realize it didn't even matter because his whole followers ditched him when they learned he was a bender, even though he could just say "The spirits are saving me!" and fix everything, then you realize his whole backstory makes his actions make even less sense now, like how he was going to deal with entire armies instead of single cities and why he hated benders when his whole life, from his perspective, his father was a non-bender.
In short, he's a dumb character written by dumb writers.