Ante-Nicene Fathers Volume VI
Gregory Thaumaturgus: Part II: Dubious or Spurious Writings: On the Subject of the Soul
As the Elucidation points out, this short essay is much more philosophy than theology and more reflective of an Aristotle than a Clement. And while the method is interesting (the soul is incorporeal, if it weren't... because it is... etc), it can be a bit dense here and there. So one to maybe skim, but not skip all together.