Sforno on Exodus 3:2/ספורנו על שמות ג׳:ב׳

1וירא מלאך ה' אליו, in a prophetic vision. When angels appear to humans in human garb this is not considered a prophetic vision, i.e. it is something of a lower order of Divine manifestation. Divine communications to Avraham, Lot, Bileam, and others like them are not described as וירא, vayeyrah, “it appeared.” However, the recipient is described as וירא, “he saw,” i.e. he is described only in his active role, not his role as receptacle of G’d’s communication. Examples of the latter kind of communication occur in Genesis 18,2 as well as in Genesis 19,1 and in Numbers 22,31.

2וירא והנה הסנה בוער באש, it kept burning; This phenomenon indicated the prophetic nature of the experience. Unless the angel had been within the bush, this could not have happened as something natural. The fire Moses saw burning enveloped the angel. The implied message was that the righteous members of the Jewish people, who are themselves angels of G’d, i.e. His messengers on earth, and who are surrounded by the Egyptian nation who treated them as burning thistles or less, would themselves become subject to this fire when enduring the ten plagues, but would remain unharmed by all those plagues. This is what Moses was taught when he saw והסנה איננו אוכל. it was not consumed by the flames which kept burning. The level of Moses’ prophecy at that time was not yet at the level it would be later on. The very fact that the Torah describes Moses as being even afraid to look at the spectacle before his eyes is proof of this (compare verse 6). From the day the Torah was given, as the Torah testifies in Numbers 12,8 ותמונת ה' יביט, G’d extended the power of Moses’ prophetic visions so that He shows him a visual image of G’d. The entire Jewish people had had a brief revelation of G’d’s glory at Mont Sinai only. Their power of endurance was so limited even at that time that the Torah reports them as saying that they could not even endure hearing the voice of the Lord, not to speak of enduring a visual image. Only Moses was able to retain the level of prophecy which the entire nation experienced during the revelation at Mount Sinai. This is the meaning of Deuteronomy 5,27-28 שובו לכם לאהליכם ואתה פה עמוד עמדי, “you (pl.) go back to your tents, and you (sing.) remain standing here beside Me.” This is also borne out by Exodus 20,18 ויעמוד העם מרחוק, “the people stood at a distance,” followed by ומשה נגש, “whereas Moses approached.” (to the cloud within which the glory of G’d was enveloped). Moses’ level of prophecy from that time on remained on the level known as פנים אל פנים, “face to face,” i.e. direct, not indirect. G’d told Miriam and Aaron there that He does not speak to Moses in riddles but by showing him a visual image (Numbers 12,8)