Jacob ben Jacob ha-Kohen, “The Commentary on Ezekiel’s Chariot by R. Jacob ben Jacob ha-Kohen of Castile,” ed. A. Farber, p. 3

Jewish Mysticism
The names above are the true essence, and they are divine powers hewn from the quarry of the intelligible light and from the pure, holy wondrous light. They are appointed to do everything, and every action is realized through them. They are interpreted truthfully by the holy prophets, the great sages, and the select few who make use of them in all good things before the Holy One, blessed be He, and not for another matter that is not the will of God. … All this comes to teach you that the name above with the true essence are hewn from the quarry of the light of life, for the intelligible grades are called kings and their glorious names are called princes. He who knows and comprehends the essence of the names, and knows how to mention them properly and correctly, as they are mentioned by the angels, his prayer is immediately received and approved. The enlightened will comprehend this secret that I have revealed concerning the matter of the name.

Translated by Elliot Wolfson in Through a Speculum that Shines- Vision and Imagination in Medieval Jewish Mysticism, Princeton- Princeton University Press, 1994.