A heathen once pressed Rabban Gamliel with a question he thought would trip up the Rabbi. Why, he asked, did the God of Israel reveal Himself to Moses out of a bush? There are cedars in Lebanon, there are palms in Jericho, there are great oaks on the hills of Bashan. Why should the voice come out of something as thorny and low as the s'neh, the bramble, that grew in the wilderness of Midian (Exodus 3:2)?
Rabban Gamliel gave a single sentence in reply, preserved in Exodus Rabbah 2:5 and collected as exemplum 42 in Moses Gaster's 1924 Exempla of the Rabbis. To show that God is everywhere.
That is the whole answer, and it is devastating in its simplicity. A cedar would have suggested majesty. A palm would have suggested elegance. A great oak would have suggested stability. Each of these would have taught Moses something about God, but it would also have taught him something false, that God's presence prefers a certain kind of vessel. The thornbush, the scraggliest, least honored, most overlooked shrub in the desert, teaches instead that the divine voice can choose any container at all. If God can speak from a bramble, then no place is too common and no person is too small.
The rabbinic imagination often extended this teaching. The Shekhinah, the Divine Presence, rests in synagogues and in sickrooms, in courts of justice and in the hut of the poor. Rabban Gamliel's one-line answer is the seed of an entire Jewish theology of immanence. The question the heathen asked was meant to be mocking. The answer he received was the first line of a sermon the sages have been preaching for two thousand years.