This is how I always viewed it. There is the soul & then the spirit. The soul is what gets reincarnated, its the lessons, events, traits, ect that we are meant to carry into the next turn we get on earth. The spirit is like a person's essence, it's what would remain behind as a ghost if they were to stay behind for some reason. As to how there are so many diffrent people, this is the phrase 'old soul" & "new soul" come into play. Just like all energy, souls are being created & destroyed. Just my view though.