Jesus promise to the disciples the holy spirit (gnosis):"Because everyone will be salted with fire", Mark 9:49. Jesus in the Gospels tells us about the daily things of life: the bread (John 6), the door (John 10: 9), the good shepherd (John 10:11). Fire is a symbol of purification and enlightenment, let us remember the tongues of fire at Pentecost, in Acts 2: 1-13.The salt symbolizes the taste for wisdom (Matthew 5:13).Salt and fire are symbols of the Holy Spirit, this transmuting action has a name in philosophy: Gnosis. Gnosticism, which cultivated ideas about Gnosis, was a current within Christianity during the first centuries.
Gnosis (born of the spirit), that is, receiving the holy spirit, requires an examination of conscience asking God for wisdom like King Solomon in the book of Kings, is that so  that the essence of man (reason) is transformed by conserving the substance (person), the holy spirit transforms the immaterial substance of man, granting the listening.
Jesus tells us to be born again to see the Kingdom of God in his dialogue with Nicodemus, John 3, this dialogue describes the importance of "receiving the spirit", the divine substance, to receive the perfection of eternal life (contemplative activity): "This is eternal life that they may know you the only true God", John 17:3. We see the kingdom of God through the eye of the mind, the eye of the spirit.
Gnosis is the transformation of the reason, is repentance of the heart, is the transmutation of the love of the soul (Philia) in the love of the spirit (Agape). The salt and the fire are simbols of the Gnosis, the salt as the wisdom has its own flavor, the fire represents the energy from God. The salt and the fire consume the Gnosis and his power.
With the Gnosis arise three spiritual gifts: the spiritual gift of Understanding (reason that loves the good), spiritual gift of discernment, and spiritual gift of Wisdom (love for the virtue and the true).
Leading the way to the fruits of the spirit, through the spiritual gift of Perseverance and the spiritual gift of eternal life (contemplative activity). In some forms of Christianity in particular the Roman Catholic Apostolic religion, the sacrament of confirmation represents this transformation of man.