The cells of the epiphysis have a strong resemblance to the photoreceptor cells of the actual eye and it is believed to be a "living fossil" that represents evolution’s earlier approach to photoreception. That is why is really called the third eye.
According to Rene Descartes who dedicated a lot of time in the study of the pineal gland :
“My view is that this gland is the principal seat of the soul, and the place in which all our thoughts are formed. The reason I believe this is that I cannot find any part of the brain, except this, which is not double. Since we see only one thing with two eyes, and hear only one voice with two ears, and in short have never more than one thought at a time, it must necessarily be the case that the impressions which enter by the two eyes or by the two ears, and so on, unite with each other in some part of the body before being considered by the soul. Now it is impossible to find any such place in the whole head except this gland; moreover it is situated in the most suitable possible place for this purpose, in the middle of all the concavities; and it is supported and surrounded by the little branches of the carotid arteries which bring the spirits into the brain.” (29 January 1640, AT III:19-20, CSMK 143)
It is now believed that the pineal gland, plays a major role in the way we perceive the world around us. Moreover, research has shown that a number of chemicals damage the epiphysis such as fluoride, sweeteners, food coloring and taste enhancers."For he [Descartes] maintained, that the soul or mind is specially united to a particular part of the brain, namely, to that part called the pineal gland, by the aid of which the mind is enabled to feel all the movements which are set going in the body, and also external objects, and which the mind by a simple act of volition can put in motion in various ways...Such is the doctrine of this illustrious philosopher (in so far as I gather it from his own words) ; it is one which, had it been less ingenious, I could hardly believe to have proceeded from so great a man. Indeed, I am lost in wonder, that a philosopher, who had stoutly asserted, that he would draw no conclusions which do not follow from self-evident premisses, and would affirm nothing which he did not clearly and distinctly perceive, and who had so often taken to task the scholastics for wishing to explain obscurities through occult qualities, could maintain a hypothesis, beside which occult qualities are commonplace. What does he understand, I ask, by the union of the mind and the body?" (Baruch de Spinoza, Ethics; part 5)
This tiny organ has without a question great secrets to reveal.