God has a reason for not showing His glory to Moses. He said to him: "When I revealed Myself to thee in the burning bush, thou didst not want to look upon Me; now thou are willing, but I am not."
The cave in which Moses concealed himself while God passed in review before him with His celestial retinue, was the same in which Elijah lodged when God revealed Himself to him on Horeb. If there had been in it an opening even as tiny as a needle's point, both Moses and Elijah would have been consumed by the passing Divine light, which was of an intensity so great that Moses, although quite shut off in the cave, nevertheless caught the reflection of it, so that from its radiance his face began to shine. Not without great danger, however, did Moses earn this distinction; for as soon as the angels heard Moses request God to show him His glory, they were greatly incensed against him, and said to God: "We, who serve Thee night and day, may not see Thy glory, and he, who is born of woman, asks to see it!" In their anger they made ready to kill Moses, who would certainly have perished, had not God's hand protected him from the angels. Then God appeared in the cloud.