I believe each of us is a much vaster Being than we appear in this physical plane; that we incarnate in a limited way because that is the nature of Space/Time, where we perceive things in a linear progression of events. The larger Entity we are has various names in various cultures, but in most spiritual paths there is this belief in a larger self, which manifests only partially as the personality.
We come here to learn something; the family we choose provides the genetic material to build a body similar to the ones we have created in past incarnations, and also the family gives us experience of a certain culture, religion and language, each of which gives new insights into the human condition and through these experiences we become more and more rounded in our beliefs, although during any specific incarnation we may express sectarian views.
After what we call "death", the smaller personality is re-absorbed into the larger self, and the experiences are digested; whatever we have done, felt, thought, and said, is analyzed for its worth to the larger self, and incorporated into the growing body of knowledge for that stream, or thread, which is continuing onward. Some call this the Soul, or Atman.
If we have developed the ability to be consciously aware of and united to the Higher Self, which some would call Buddha and others might term the Christ consciousness, we can participate in the planning of the next incarnation. Before that point, incarnation is given to us by the Higher Self, who has a lesson plan in Mind. If we are on that automatically-generated path, we become unconscious shortly after death, and the process is not conscious.
During the incarnation, each of us makes mistakes, and those very mistakes are the gems of experience, because we learn and grow from them. We can learn from positive acts as well, but only if they are done without ulterior motive, and only if they are done from love of self and others, and not from fear of punishment or retribution. What humans call "evil" is a huge learning experience for all of us, and it cannot be escaped on this plane of opposites. It must nevertheless be opposed. This opposition to evil builds our spiritual muscles.
For most of us, there is one major lesson in each lifetime. Those who have gone through many thousands of lessons find some form of spiritual path and follow it, not for reward but because it is an imperative, Soul-driven desire. The Path we choose is the one that is right for our Soul's work. On that Path, more lessons come in one incarnation than would usually be dealt with. Sometimes, a Soul takes a lifetime off that Path, and refuses to even consider things of the Spirit. That is a lifetime of filling in some gap or gaps that must be healed before the Soul can continue on. Many human beings who perform large and lasting service to humanity need to focus on that service, and they may not appear to be on a spiritual path.