The Spirits' Book
Book Three - Moral Laws
Chapter IX - VIII. Law of Equality
Inequality of Aptitudes
805. In passing from a higher world to a lower one, do spirits preserve the faculties they had acquired?
“Yes, we have already told you that spirits who have progressed cannot regress. As spirits they may choose a physical envelope that is more insensitive, or a position that is more uncertain, but each variation is intended to teach them a new lesson and help them to progress.” (See Q180)
The diversity of human abilities is the result of the various degrees of perfection achieved by the spirits, rather than something intrinsic to the creation of humankind. God has not created the inequality of human faculties. God permits spirits of different degrees of development to be in contact with each other, so that the more advanced may help those who lag behind, and so that all human beings may understand the law of charity that is destined to unite them.