When Moses drew near to Mount Horeb, he was aware at once that it was a holy place, for he noticed that passing birds did not alight upon it. At his approach the mountain began to move, as though to go forward and meet him, and it settled back into quietude only when his foot rested upon it. The first thing Moses noticed was the wonderful burning bush, the upper part of which was a blazing flame, neither consuming the bush, nor preventing it from bearing blossoms as it burnt, for the celestial fire has three peculiar qualities: it produces blossoms, it does not consume the object around which it plays, and it is black of color.
The fire that Moses saw in the bush was the appearance of the angel Michael, who had descended as the forerunner of the Shekinah herself to come down presently. It was the wish of God to hold converse with Moses, who, however, was not inclined to permit any interruption of the work under his charge. Therefore God startled him with the wonderful phenomenon of the burning thorn-bush. That brought Moses to a stop, and then God spoke with him.