I believe in the concept of deity, but not in the Judeo-Christian concept of God as the "man upstairs" who watches over us and decides our fates when we die. I think that if there was a conscious entity with all that power and knowledge, they would not be able to help but make their presence more overtly known to their creations. And surely if they can create a human "avatar" here on Earth, then they would do it more than once every few thousand years.
But I do believe in deity in the sense of some sort of creative intelligence, and I see all of humanity as physical manifestations of that intelligence, and our own intelligence and creative powers as proof of such. That, I believe, is where reincarnation comes in. When we die, the piece of the divine that was "us" stays around to inhabit another shell and keeps doing so until it gains enough of whatever it needs to return to the source. What that is I really can't pretend to know, but whatever it is must be gained through living and experiencing this dimension that we call "reality".
The question that someone might ask then is "why?" Why would a supreme intelligent power want to cut parts of itself away to "suffer" the kinds of things we go through in our lives? Well, the Gnostics believe that our separation is some sort of accident, and that our goal as humans is to learn enough and elevate ourselves enough in this life so that we may "figure out" how to return to the source. This philosophy, while giving some hope, is too close to the Christian view of things IMO, in that they believe that some will make it and enjoy eternity, but that most will simply perish in the attempt and cease to exist when they die. They also believe that most people are on their "last life" and that this is their last chance to figure it out. A bit of a "convenient truth" if you ask me.
That leads me to what I believe. If something like that did happen, and a supreme intelligence lost parts of itself, do you think they would leave it up to the inferior parts of itself "stuck" in the prison of physical reality to try to get out by themselves? If your toe gets cut off, do you wait for it to crawl back onto your foot? Of course not, you keep it in ice and bring it to a doctor to hopefully sew back on. Well, that's not the best analogy, because I have to assume that a supreme intelligence would have much better ways to integrate parts of itself back together, which leads me to my main idea, which is that it is possible that it purposefully lets parts of itself into the "prison" of our reality in order for it to experience things that it never would if it just stayed in it's own "dimension" (for lack of a better word). And it might separate itself into so many parts because it wants to experience every facet of this inferior dimension that it can, so it puts parts of itself in a variety of situations and predicaments.
And it might also create beings that are lower than itself, but still higher than "we" are. Beings that can more directly interact with our world on it's behalf, because it would probably be hard for it to fully comprehend our existence enough to have any meaningful interaction with it. As an analogy, think about an ant. We know what it is and how it does what it does, but can you really conceive of life as an ant? Of course not. So these "middle" beings would be what we call "gods". Ancient people had the ideas that certain deities covered different aspects of their lives and of the various forces at work on this planet. That would definitely fit in with my theory, as each entity would naturally be responsible for certain aspects of maintaining this plane of existence.
Now, if my ideas are a more "top down" approach to cosmology, where there is a supreme intelligence that created lesser intelligences, which in turn created us and every thing around us, then you could try to counter such ideas with a "bottom up" theory where everything is exactly as it appears and everything above ourselves are just wishful imaginings of a species that lives, dies, and that's it. And you could be right! We can't really know what the truth is for sure. But my ideas resonate as true to me, and that is the essence of belief and faith.