Moses had to move the sheep from place to place to find grazing for them. So, here he is on the mountain, and he sees a fire. Fire probably wasn’t uncommon in the desolate desert where dried vegetation could spontaneously catch fire. But he looks at the fire and notices that there is something different. The bush is not burning. The leaves did not curl, nor did the branches break and fall off. It’s on fire but it is not burning.
