Gnosis is associated with the Third Eye and intuitive sight or spiritual sight. It is associated with the phrase, “I SEE” because the one who has acquired Gnosis can see into the spiritual realm intuitively.

For the spiritual seeker, the most important knowledge is that of their own divine self and immortality. It is the knowledge of God. Esoteric texts hint that to know yourself, your divine Self is to know God because the human is an image of God therefore to know One is to simultaneously know the other. This knowledge of the divine Self was differentiated from scientific knowledge (Episteme) which was through Logic and Reason. This knowledge of God was called Gnosis and it was believed that Gnosis could only be gained through the help of intuition since it is impossible to know God through Reason and Logic alone. The visible universe can be known through reason and logic but God dwells in a realm beyond the physical and this realm cannot be penetrated by rationality without the help of intuition. Opening your third eye is simply opening your intuitive eye. Intuition and the third eye is the faculty through which we can know and be sure of spiritual truths even though we might find it hard to put it into words. You might feel strongly in your soul that something is true but fail to give the reason why.

Science can help us to know about the material universe but the material universe is not all there is since there is an invisible spiritual realm beyond which we can never know without intuition. Esoteric knowledge like Kabbalah and Hermeticism all seeks to point us to knowing what is beyond the physical and if you approach this knowledge desiring to know it through rationality and logic alone then you will be lost since God is beyond Logic. Therefore, for anyone who wishes to know themselves and to know God, the first step is to understand that there is more to reality than the physical and you can never know God unless he reveals himself to your rational mind through intuition. For the person who doesn’t believe in anything other than the physical and only believers in what can be rationally deciphered through Logic, they have already closed themselves to knowing God and refused to listen to the voice of intuition without which we can never know God.

To sum up, here are some quotes from the book “Intuition: Knowing beyond Logic” by Osho.

Intuition cannot be explained scientifically because the very phenomenon is unscientific and irrational. The very phenomenon of intuition is irrational.
In language it looks okay to ask, “Can intuition be explained?” But it means, “Can intuition be reduced to intellect?” And intuition is something beyond the intellect, something not of the intellect, something coming from some place where intellect is totally unaware. So the intellect can feel it, but it cannot explain it.

According to reason there are two realms of existence, the known and the unknown. And the unknown means that which is not yet known but will someday be known. But mysticism says that there are three realms: the known, the unknown, and the unknowable. By the unknowable, the mystic means that which can never be known.
Intellect is involved with the known and the unknown, not with the unknowable.

Intuition works with the unknowable, with that which cannot be known. It is not just a question of time before it will be known— unknowability is its intrinsic quality. It is not that your instruments are not fine enough or your logic not up-to-date, or your mathematics primitive— that is not the question. The intrinsic quality of the unknowable is unknowability; it will always exist as the unknowable.
This is the realm of intuition.
When something from the unknowable comes to be known, it is a jump —there is no link, there is no passage, there is no going from one point to another point. But it seems inconceivable, so when I say you can feel it but you cannot understand it, when I say such things, I know very well that I am uttering nonsense. “Nonsense” only means that which cannot be understood by our senses. And mind is a sense, the most subtle.

Intuition is possible because the unknowable is there. Science denies the existence of the divine because it says, “There is only one division: the known and the unknown. If there is any God, we will discover him through laboratory methods. If he exists, science will discover him.