The Spirits' Book
Book Two - The Spirit World
Chapter VII - Return to Physical Life
Moral and Intellectual Faculties
365. Why are some very intelligent people, whose intelligence is proof of the presence of an advanced spirit, also extremely vicious?
“Because the spirit incarnated in these individuals are inadequately purifed, and may yield to the sway of spirits who are even more inferior. A spirit advances slowly, but this progress does not take place in all directions simultaneously. It may advance intellectually at one point, and morally at another.”