מוסר אויף בראשית 28:18

The general principle of the matter: Holiness consists of one's clinging so much to his G-d that for any action he does, he will not separate nor budge from G-d, blessed be He, so that the physical things he uses will attain greater elevation than that which he diminishes in his clinging and level due to his using physical things.

Bereshit Rabbah 68,11, on Genesis 28,11: ויקח מאבני המקום, "He took from the stones of that place," comments that Jacob made an experiment. He took 12 stones and said to himself, that seeing that neither Abraham nor Isaac had founded the twelve tribes, if those stones were to fuse, it would signify that he, Jacob, was slated to do so. When he awoke he found that the stones had fused. The Torah writes: "He took the stone which he had made into his pillow" (28,18). By this he was convinced that he would become the founder of the Jewish nation. The letters of the Torah are alluded to in these stones. We read in Sefer Yetzira chapter 4, section 17: "Two stones build two houses; three stones build six houses; four stones build twenty four houses, etc." The stones are hyperbole for letters.