Just one little thought here: To believe in life after death or in "the soul"...or for that matter, in ghosts or other such paranormal or spiritual phenomena...does not necessarily make one a theist.

One could be an atheist (someone who doesn't believe in a "supreme being" or a "God" who is in charge of everything), and still believe that everyone has a soul which survives physical death, and perhaps returns again in other physical lifetimes.