Jewish Mysticism
Thus you find that the whole tribe of Levi is very sparse. Why were they so few in number? For they looked upon the Presence… The Holy One, blessed be He, said- In this world they vanished on account of the fact that they looked at My glory, as it says, “man may not see Me and live.” However, in the world-to-come, when I return My Presence to Zion, I will be revealed in My glory to all of Israel, and they will see Me and will live eternally.

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