There were good reasons for selecting the thorn-bush as the vessel for a Divine vision. It was "clean," for the heathen could not use it to make idols. God's choosing to dwell in the stunted thorn-bush conveyed the knowledge to Moses that He suffers along with Israel. Furthermore, Moses was taught that there is nothing in nature, not even the insignificant thorn-bush, that can exist without the presence of the Shekinah.
Besides, the thorn-bush may be taken as the symbol for Israel in several respects. As the thorn-bush is the lowliest of all species of trees, so the condition of Israel in the exile is the lowliest as compared with that of all the other nations, but as the thorn-bush releases no bird that alights upon it without lacerating its wings, so the nations that subjugate Israel will be punished. Also, as a garden hedge is made of the thorn-bush, so Israel forms the hedge for the world, the garden of God, for without Israel the world could not endure.
Furthermore, as the thorn-bush bears thorns and roses alike, so Israel has pious and impious members, and as the thorn-bush requires ample water for its growth, so Israel can prosper only through the Torah, the celestial water. And the thorn-bush, the leaf of which consists of five leaflets, was to indicate to Moses that God had resolved to redeem Israel only for the sake of the merits of five pious men, Abraham, Isaac, Jacob, Aaron, and Moses.
The numbers represented by the letters composing the Hebrew word for thorn-bush, Seneh, add up to one hundred and twenty, to convey that Moses would reach the age of one hundred and twenty years, and that the Shekinah would rest on Mount Horeb for one hundred and twenty days. Finally, in order to give Moses an illustration of His modesty, God descended from the exalted heavens and spake to him from a lowly thorn-bush instead of the summit of a lofty mountain or the top of a stately cedar tree.