I think we exist as a part of a greater reality that is God. We are a part of his being. Whether he has need for us is debatable. I'm pretty sure the greater reality I call God would get along just fine without us, though. I'm not sure we have a particular purpose OAT ... I do believe we have been given an opportunity to be co creators of something great. We exist no matter the reason "why" and I fully believe it is in our power and that it is our responsibility to establish (Maybe re-establish) a paradise on earth.