Zohar 3:79a

Jewish Mysticism
It has been taught- “Do not come near a woman during her period of uncleanness to uncover her nakedness” (Lev. 18-19). R. Judah taught- The generation in which R. Simeon bar Yohai dwells is all righteous, all pious, all fearers of sin. The Presence dwells amongst them unlike other generations. Therefore these [esoteric] matters are made explicit and not hidden. In other generations this was not the case and matters pertaining to the supernal secrets could not be revealed, and those who knew them were afraid [to disclose them]. When R. Simeon communicated the secret of that verse [Lev. 18-19] the eyes of the comrades shed tears, and all that he said was revealed in their eyes, as it is written, “With him I speak mouth to mouth, plainly and not in riddles” (Num. 12-8).

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