Now concerning mental faculties, they are in truth of the inherent properties of the soul, even as the radiation of light is the essential property of the sun. The rays of the sun are renewed but the sun itself is ever the same and unchanged. Consider how the human intellect develops and weakens, and may at times come to naught, whereas the soul changeth not. For the mind to manifest itself, the human body must be whole; and a sound mind cannot be but in a sound body, whereas the soul dependeth not upon the body. It is through the power of the soul that the mind comprehendeth, imagineth and exerteth its influence, whilst the soul is a power that is free. The mind comprehendeth the abstract by the aid of the concrete, but the soul hath limitless manifestations of its own. The mind is circumscribed, the soul limitless. It is by the aid of such senses as those of sight, hearing, taste, smell and touch, that the mind comprehendeth, whereas, the soul is free from all agencies. The soul as thou observest, whether it be in sleep or waking, is in motion and ever active. Possibly it may, whilst in a dream, unravel an intricate problem, incapable of solution in the waking state. The mind, moreover, understandeth not whilst the senses have ceased to function, and in the embryonic stage and in early infancy the reasoning power is totally absent, whereas the soul is ever endowed with full strength. In short, the proofs are many that go to show that despite the loss of reason, the power of the soul would still continue to exist. The spirit however possesseth various grades and stations.
(‘Abdu’l-Bahá, Bahá’í World Faith, p. 337-338)