The treatise "On the Soul" by Niketas Stithatos is a key work for understanding the material of a thematic subject that particularly occupied Byzantine thought, such as the creation of angels, the visible world and humans, the essence of the soul, and the state of the soul after the death of the body.

With knowledge of the Scriptures and earlier theological literature, Niketas Stithatos defines the immaterial nature of angels in relation to humans and their material nature in relation to God, the describable, the invisible, the intellectual and immortal, etc., properties that were granted to them by God's grace, and describes their services.

Concerning the creation of the world, he advocates the Christian understanding of the threefold creation (intelligible - sensible world - composition of man in body and soul). From this point onward, the Soul, the spirit of the body, is bound to the body and lights the way for its salvation.