וַיִּפְגַּ֨ע בַּמָּק֜וֹם וַיָּ֤לֶן שָׁם֙ כִּי־בָ֣א הַשֶּׁ֔מֶשׁ וַיִּקַּח֙ מֵאַבְנֵ֣י הַמָּק֔וֹם וַיָּ֖שֶׂם מְרַֽאֲשֹׁתָ֑יו וַיִּשְׁכַּ֖ב בַּמָּק֥וֹם הַהֽוּא׃
וַיַּשְׁכֵּ֨ם יַעֲקֹ֜ב בַּבֹּ֗קֶר וַיִּקַּ֤ח אֶת־הָאֶ֙בֶן֙ אֲשֶׁר־שָׂ֣ם מְרַֽאֲשֹׁתָ֔יו וַיָּ֥שֶׂם אֹתָ֖הּ מַצֵּבָ֑ה וַיִּצֹ֥ק שֶׁ֖מֶן עַל־רֹאשָֽׁהּ׃
For many of us, these verses evoke the image of Jacob's quarreling stones -- each demanding, "upon me let this righteous man lie his head," until God fused them together (Rashi, Gen. 28:11 following Bereshit Rabba and Hulin 91b). A memorable story by itself with an echo of ancient Israelite mythology, this midrash is also a moving metaphor for the twelve tribes of Israel uniting under the banner of their forefather Jacob (see Bereshit Rabba and Pirke de-Rabbi Eliezer for the tradition of twelve stones and its explicit symbolism).
But why did Jacob need a stone in the first place? וַיָּ֖שֶׂם מְרַֽאֲשֹׁתָ֑יו may seem to suggest he wanted to prop up his head on a stone pillow. And on one level, this makes sense. Jacob later says that he escaped from Esau carrying only his walking stick (Gen. 32:10). Even if this was poetic exaggeration, Jacob would still have had no time to pack unnecessary belongings, certainly not cushions or extra garments for padding his campsite. A pillow of stone befits his desperate and spartan condition at the time.
The peshat-oriented exegetes (e.g., Rashbam, Ibn Ezra, Bekhor Shor), of course, don't feel bound to read מֵאַבְנֵ֣י הַמָּק֔וֹם as multiple stones; they insist that Jacob took just one stone of many in the area. (Interestingly, the King James Version translation follows Rashi: "and he took of the stones of that place, and put them for his pillows, and lay down in that place to sleep.")
The Torah tells a story about a random rock because of its special destiny. After sleeping beside the rock, and awaking from his famous dream, Jacob dedicates it as a מצבה (a stele or monument), anoints it with oil (an act of consecration) and vows that upon his safe return from Haran he will sacrifice thanksgiving offerings to God in that very spot, the site of a future temple.
But why did Jacob need a stone in the first place? וַיָּ֖שֶׂם מְרַֽאֲשֹׁתָ֑יו may seem to suggest he wanted to prop up his head on a stone pillow. And on one level, this makes sense. Jacob later says that he escaped from Esau carrying only his walking stick (Gen. 32:10). Even if this was poetic exaggeration, Jacob would still have had no time to pack unnecessary belongings, certainly not cushions or extra garments for padding his campsite. A pillow of stone befits his desperate and spartan condition at the time.
Still, the word מְרַאֲשׁוֹת in the Bible doesn't always, or possibly ever, mean "under the head." Instead, it appears to mean "beside the head." The biblical usage includes, for example, the following (I Samuel 26:7, 11-12): וַחֲנִית֥וֹ מְעוּכָֽה־בָאָ֖רֶץ מְרַאֲשֹׁתָ֑יו -- "his spear stuck in the ground at his head" -- definitely not under his head! (see also Mandelkern's Concordance, p. 1065, which defines מְרַאֲשׁוֹת as "the opposite of מַרְגְּלֹתָיו," i.e., at the feet, rather than on the feet).
It seems very likely that Jacob's stone, or stones, were for warmth. Ancient travelers sleeping outside in the cool night air, especially in the desert, could take advantage of the heat that radiates, well into the night, from sunbaked rocks. Jacob may have also deliberately avoided lighting a fire at night so as not to draw attention from Esau and his men who, Jacob would have feared, were already pursuing him.
If so, then the Midrash, rather than the peshat commentaries, may have gotten it right after all. For maximum radiant heat, Jacob would no doubt have gathered as many large stones as he could.
Jacob's descendants, an imperfect union of often warring tribes, are fortunate that those honor-hungry, self-centered stones ultimately, if involuntarily, made peace with each other.