Mind

And each one of these members hath its own special function. The mind force -- whether we call it pre-existent or contingent -- doth direct and co-ordinate all the members of the human body, seeing to it that each part or member duly performeth its own special function. If, however, there be some interruption in the power of the mind, all the members will fail to carry out their essential functions, deficiencies will appear in the body and the functioning of its members, and the power will prove ineffective.

‘Abdu’l-Bahá, Selections from the Writings of ‘Abdu’l-Bahá, p. 48

But the mind is the power of the human spirit. Spirit is the lamp; mind is the light which shines from the lamp. Spirit is the tree, and the mind is the fruit. Mind is the perfection of the spirit, and is its essential quality, as the sun's rays are the essential necessity of the sun.

‘Abdu’l-Bahá, Bahá’í World Faith, p. 316

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.

‘Abdu’l-Bahá,

Consider what it is that singles man out from among created beings, and makes of him a creature apart. Is it not his reasoning power, his intelligence? Shall he not make use of these in his study of religion?

‘Abdu’l-Bahá, Paris Talks, p. 144

How can man believe that which he knows to be opposed to reason? Is this possible? Can the heart accept that which reason denies? Reason is the first faculty of man, and the religion of God is in harmony with it.

‘Abdu’l-Bahá, The Promulgation of Universal Peace, p. 231

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.

‘Abdu’l-Bahá, Bahá’í World Faith, p. 337