Moses de Leon, MS Vatican 283, fol. 170a

“And the creatures ran to and fro, in the appearance of a flare” (Ezek. 1-14). From here is the mystery of the supernal chariot, the speculum that shines, the splendor devoid [of form] which is not comprehended by mental vision, except in a concealed manner, in the hidden depth, in the manner of the splendor and radiance of that which is comprehended in the concealment and rotation [of the eye]. When the eye is closed and rolls around a concealed splendor is seen momentarily, for it does not settle down to be seen [in a fixed way]. So it is by the supernal creatures–they are the splendor of the speculum that shines which does not settle down to be seen, but rather “runs to and fro,” as the revolving of the water in a plate when placed against the light of the sun. The flame of the sun sparkles in [a manner of] “running and returning,” but does not settle down in one place. So it is with respect to those creatures as we have said.

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