My are belief is that in the very beginning humans were male and female in one body. One head with two faces. Four arms. Two legs. Reproductive organs of both male and female. Zeus became enraged at the human race from jealousy and so he split humans info males and femalescas we are today. This brought about soulmates. And each life you and your soulmate will live at the same time. The same life. The goal is to find each other and be with each other. There is another goal that is to try to perfect your life every life. Perfect for your self and perfect with your soulmate. You will change every life in any possible way. Race. Personality. Location. Appearance. Etc. Usually in small. Details. Some times majorly. When one thing is perfected it will stay that way. Once every thing is perfected you will be reincarnated the same every time. With each life that life gets embedded within the soul. The lives that follow all have the potential to unlock memories, energies, abilities, and the like from previous lives. This comes from not only remembering past lives but also tapping into those lives through the soul. You may even need to heal those lives as well.
This is merely my opinion and personal belief on reincarnation and how it is. Disagree with it or agree. Every one has a different believe.