Gnosis is a psychological resolution through which we reach the likeness of God. The classical philosophy, in particular, Aristotle and Plato do not mention Gnosis, but in the bible, it is well documented with another name: "born of the spirit": "flesh gives birth to flesh, but the Spirit gives birth to spirit", John 3:6; "receive the Holy Spirit": "all of them were filled with the Holy Spirit", Acts 2:4
Why gnosis occurs? Jesus explains the origin of gnosis, in a dialogue about love with his disciple Peter: "Jesus said to Simon Peter: Simon, son of John, do you Agape more than these? Yes, Lord, you know that I philia you" John 21:15-16
Philia describes the rational man, philia is the love of friendship, the love mixed with virtue. The rational man is in an intermediate state between good and evil.
Agape is the love projected to the whole creation of God, Agape is the love of the spirit, the gift of love. When we receive Agape, we receive the likeness to God.
The book "Tractate of the perfect and moral virtues", you can download it for free, if you follow the link in the profile, explains this in another way:
The level of consciousness changes with the level of love: "Jesus replied, Very truly I tell you, no one can see the kingdom of God unless they are born again." John 3:3. This change of mind is an opening of the intelligence: "Then he opened their minds so they coul understand the Scriptures", Luke 24:45
With gnosis we receive three spiritual gifts: the gifts of knowledge, wisdom and discernment. We must now differentiate gnosis with the opening of the third eye.
After gnosis contemplative activity appears and as a consequence of contemplation the third eye opens. Gnosis and the third eye are not the same. When we open the third eye we receive the guide of God.
A practical case of this are the three wise men who visit Jesus (Matthew 2:1-12), they have the guidance of God and avoid dangers fulfilling their mission. They know how to interpret the signs of the sky, the comet, and dreams in which they are warned of Herod.
With the Gnosis arises the "doctor of wisdom", magi or magus in ancient persian means that. The "doctor of widom" when he governs establishes the government of God among men.