The soul, therefore, is a living essence, uncomplicated, incorporeal, invisible – in its proper nature – to the eyes of the body, immortal, reasoning and intelligent, formless, making use of an organic body and being the source of its powers of life, growth, sensation and generation, the intellect being its purest part though not in any way alien to it (as the eye is to the body, so the intellect is to the soul). It has power over itself, its volition and energy, and is mutable, i.e. able to be changed, because it is created. All of these features are natural to it through the Grace imparted by its Creator, and its being and nature are thus because of this same Grace which it has received.
Based on Saint John of Damascus