From :

The Secret Teachings of All Ages.

Manly P. Hall

Chapter:

The human body in symbolism.

As light bears witness of life-which is its source-so the mind bears witness of the spirit, and activity in a still lower plane bears witness of intelligence. Thus the mind bears witness of the heart, while the generative system, in turn, bears witness of the mind. Accordingly, the spiritual nature is most commonly symbolized by a heart; the intellectual power by an OPENED EYE, symbolizing the pineal gland or Cyclopean eye, which is the two-faced Janus of the pagan Mysteries; and the generative system by a flower, a staff, a cup, or a hand.

While all the Mysteries recognized the heart as the center of spiritual consciousness, they often purposely ignored this concept and used the heart in its exoteric sense as the symbol of the emotional nature, In this arrangement the generative center represented the physical body, the heart the emotional body, and the brain the mental body. The brain represented the superior sphere, but after the initiates had passed through the lower de¬ grees they were instructed that the brain was the proxy of the spiritual flame dwelling in the innermost recesses of the heart. The student of esotericism discovers ere long that the ancients often resorted to various blinds to conceal the true interpretations of their Myster¬ ies. The substitution of the brain for the heart was one of these blinds