Kommentar zu Schemot 34:33

ויתן על פניו מסוה AND HE PUT A VEIL ON HIS FACE — Render it (מסוה) as the Targum does: בית אפי, a cover for his face. מסוה is an Aramaic expression (from the root סוי, “to look”). It occurs in the Talmud (Ketubot 62b) “her heart perceived (סּוי), and again in Ketubot 60a “הוה קא מסוה לאפה”, where מסוה is an expression for looking: “he looked into her face”, i. e. he gazed at her. Here, too, מסוה denotes a cloth that was put in front of the face and of the region of the eyes. And out of reverence for the “rays of glory” — that not everybody should feast himself on them — Moses used to put the veil in front of them (the eyes), but took it off during the time when he spoke to Israel, and during the time when the Omnipresent conversed with him until the moment when he was going out and also when he went out he went out without the veil.

He placed a cover over his face. Moshe, in his great humility, was embarrassed when people gaped at the radiance of his face. But whenever he received instruction from God he was required to remove it, in keeping with the Sages’ principle that one who is prone to shame cannot learn (Pirkei Avos 2:5).

ויכל משה מדבר אתם, but while he was still speaking to them he did not wear the cloth. This corresponds to Isaiah 30,20 “your eyes should look at your teachers.” As our sages explained (Eyruvin 13, Rabbi Yehudah Hanassi speaking) “if I had looked at his (Rabbi Meir’s) teacher’s face instead of merely at his back I would have been even more learned.”)