A Commentary, Critical, Practical, and Explanatory on the Old and New Testaments, by Robert Jamieson, A.R. Fausset and David Brown  at sacred-texts.com
exo 3:1DIVINE APPEARANCE AND COMMISSION TO MOSES. (Exo. 3:1-22)
Now Moses kept the flock--This employment he had entered on in furtherance of his matrimonial views (see on Exo 2:21), but it is probable he was continuing his service now on other terms like Jacob during the latter years of his stay with Laban (Gen 30:28).
he led the flock to the backside of the desert--that is, on the west of the desert [GESENIUS], assuming Jethro's headquarters to have been at Dahab. The route by which Moses led his flock must have been west through the wide valley called by the Arabs, Wady-es-Zugherah [ROBINSON], which led into the interior of the wilderness.
Mountain of God--so named either according to Hebrew idiom from its great height, as "great mountains," Hebrew, "mountains of God" (Psa 36:6); "goodly cedars," Hebrew, "cedars of God" (Psa 80:10); or some think from its being the old abode of "the glory"; or finally from its being the theater of transactions most memorable in the history of the true religion to Horeb--rather, "Horeb-ward."
Horeb--that is, "dry," "desert," was the general name for the mountainous district in which Sinai is situated, and of which it is a part. (See on Exo 19:2). It was used to designate the region comprehending that immense range of lofty, desolate, and barren hills, at the base of which, however, there are not only many patches of verdure to be seen, but almost all the valleys, or wadys, as they are called, show a thin coating of vegetation, which, towards the south, becomes more luxuriant. The Arab shepherds seldom take their flocks to a greater distance than one day's journey from their camp. Moses must have gone at least two days' journey, and although he seems to have been only following his pastoral course, that region, from its numerous springs in the clefts of the rocks being the chief resort of the tribes during the summer heats, the Providence of God led him thither for an important purpose.
exo 3:2the angel of the Lord appeared unto him in a flame of fire--It is common in Scripture to represent the elements and operations of nature, as winds, fires, earthquakes, pestilence, everything enlisted in executing the divine will, as the "angels" or messengers of God. But in such cases God Himself is considered as really, though invisibly, present. Here the preternatural fire may be primarily meant by the expression "angel of the Lord"; but it is clear that under this symbol, the Divine Being was present, whose name is given (Exo 3:4, Exo 3:6), and elsewhere called the angel of the covenant, Jehovah-Jesus.
out of the midst of a bush--the wild acacia or thorn, with which that desert abounds, and which is generally dry and brittle, so much so, that at certain seasons, a spark might kindle a district far and wide into a blaze. A fire, therefore, being in the midst of such a desert bush was a "great sight." It is generally supposed to have been emblematic of the Israelites' condition in Egypt--oppressed by a grinding servitude and a bloody persecution, and yet, in spite of the cruel policy that was bent on annihilating them, they continued as numerous and thriving as ever. The reason was "God was in the midst of them." The symbol may also represent the present state of the Jews, as well as of the Church generally in the world.
exo 3:4when the Lord saw that he turned aside to see--The manifestations which God anciently made of Himself were always accompanied by clear, unmistakable signs that the communications were really from heaven. This certain evidence was given to Moses. He saw a fire, but no human agent to kindle it; he heard a voice, but no human lips from which it came; he saw no living Being, but One was in the bush, in the heat of the flames, who knew him and addressed him by name. Who could this be but the Divine Being?
exo 3:5put off thy shoes--The direction was in conformity with a usage which was well known to Moses, for the Egyptian priests observed it in their temples, and it is observed in all Eastern countries where the people take off their shoes or sandals, as we do our hats. But the Eastern idea is not precisely the same as the Western. With us, the removal of the hat is an expression of reverence for the place we enter, or rather of Him who is worshipped there. With them the removal of the shoes is a confession of personal defilement and conscious unworthiness to stand in the presence of unspotted holiness.
exo 3:6I am the God . . . come down to deliver--The reverential awe of Moses must have been relieved by the divine Speaker (see Mat 22:32), announcing Himself in His covenant character, and by the welcome intelligence communicated. Moreover, the time, as well as all the circumstances of this miraculous appearance, were such as to give him an illustrious display of God's faithfulness to His promises. The period of Israel's journey and affliction in Egypt had been predicted (Gen 15:13), and it was during the last year of the term which had still to run that the Lord appeared in the burning bush.
exo 3:10Come now therefore, and I will send thee--Considering the patriotic views that had formerly animated the breast of Moses, we might have anticipated that no mission could have been more welcome to his heart than to be employed in the national emancipation of Israel. But he evinced great reluctance to it and stated a variety of objections [Exo 3:11, Exo 3:13; Exo 4:1, Exo 4:10] all of which were successfully met and removed--and the happy issue of his labors was minutely described.