@William,
Hello,
This question is basically the same as "What is the purpose of life?", and to me, the answer is: There is no purpose. It just is. I think all life comes from a fundamental source(a godforce), and it is the most basic thing that has always existed from which life is possible, and to ask if it has a purpose, would be like implying that there was something before it, or along with it, and there isn't.
Instead of asking your question, think of it this way instead: Either you have always existed, or you came into existence at some time in the past(possibly before the life you are living now). The latter seems reasonable, so lets look at that. Now at one time you did not exist, and now you do. What this means is that there was a particular configuration of matter and energy that made you a unique being(personality), perhaps your conciousness emerges from your DNA somehow, or is a division of this godforce i mentioned, or whatever. The point is that at one time you did not exist and now you do, so over an infinite amount of time, after you die. The same set of circumstances that arouse to make you what you are now, could arise again. Also, when you are dead, time ceases to exist, so being dead for 100 billion years and then being re-born would seem instantaneous.
So anyways, aside from the godforce. The purpose of any life, whether it be after death or not, to me, would be to experience. In this reality, as sentient beings we experience through are 5 senses, and i suppose other experience such as feelings.