“Despite later distrust and suppression by Pauline orthodoxy, mysticism flourished in the early church.
Master Yeshuvah taught one set of teachings openly to the public, and another set of secret teachings privately to his most advanced disciples. The Gospels themselves attest to this, and Clement of Alexandria wrote about such a secret teaching as late as the third century CE.
Of all the Christian mystical literature, the most enigmatic and passionately discussed is the Revelation of John. It opens with a description of John’s vision of the Ancient of Days with fiery eyes and a two-edged sword coming from his mouth, etc.”
–Daniel Feldman, Qabala: The Mystical Heritage of the Children of Abraham, 2001, pg. 71.