A soul is a consciousness, by definition, but that alone didn't provide the consciousness any way to express itself. It still needed an astral body to operate upon and begin the thought process—but that wasn't enough, either, since any thoughts produced would just dissipate into the wind. That's where the spiritual body came in, to record and keep those thoughts captive. Even that was still a virtual memory, though, not any kind of permanent storage— and so we come to the material body.