In this week's Parsha, we find the instructions to have two small stones that would be part of the garment which would go on the Kohein Gadol's shoulders (שמות כ"ח:ט'-י"ב). Each stone would have the name of six tribes of Bnai Yisrael engraved into it, and they would serve as a remembrance. The question is, a remembrance of what, and for whom? Perhaps we can see from the fact that the Posuk writes that Aharon should carry the names of the tribes on his two shoulders as a remembrance before Hashem (שם פסוק י"ב) that the remembrance is in fact for Hashem. But the earlier phrase in that Posuk (שם) says that the two stones are to be placed on the shoulder pieces of the Eiphod as remembrance stones for Bnai Yisrael. Who, then, who is the remembrance for, Hashem or Bnai Yisrael, or both?
Perhaps there is a connection between these stones and an event in Sefer Bereishis, also involving stones. The Torah describes that when Yaakov left Beer Sheva and went to Charan, he was traveling and it became dark, and he needed a place to sleep. The Torah then says that he took some stones and placed them under his head (בראשית כ"ח:י"א). It was during this sleep that he had a dream where he saw a ladder reaching from the ground to the sky with angels ascending and descending it, and that Hashem told him that He is the G-d of his father and grandfather and promised him that his descendants would be like the dust of the earth. Hashem also indicated that he would protect Yaakov wherever he went and would eventually bring him back to Eretz Yisrael, and that He would not turn away until he had fulfilled His promise (שם פסוקים י"ג-ט"ו). The Torah then says that when Yaakov woke up, he took the stone that he had kept by his head and used it for an altar on to which he poured oil. He then promised a tenth of his profits to Hashem on condition that Hashem would help him return in peace from the trip he was taking and provide him with food and clothes, adding that this stone would become a house for Hashem (שם פסוקים ט"ז-כ"ב).
According to the Midrash, Yaakov originally took twelve stones to surround himself and to use as a pillow for himself. But why twelve stones? Wouldn't two stones have been enough to support him, with one on one side above his shoulder and one on the other side, while his head would lay between the two, but on them like a pillow? Why did he need so many? Perhaps this may relate to the stones worn on the shoulders of the Kohein Gadol, which had the names of the twelve tribes engraved in them. The number twelve corresponds to Yaakov's children, and perhaps that is the connection: just as the two stones represent the twelve tribes, so too the stones around Yaakov represented the (future) twelve tribes. The Kohein Gadol also had twelve stones in his Choshen (שמות שם פסוקים י"ז-כ"א); this too may relate to the twelve stones on which Yaakov slept.
Perhaps we can now understand why the stones on the Kohein Godol were called a remembrance, as stated above. Obviously, they are for Hashem to remember the twelve Shevatim, because their names are all there. But they also remind Hashem to remember his promise to Yaakov that his descendants would multiply like the dust on the earth, and spread out in all directions. Hashem would remember this promise every time He "looked" at the Kohein Godol. Of course, Hashem doesn't really need reminders, but in view of the fact that according to many Meforshim the Jews had just committed the terrible sin involving the golden calf, this remembrance may serve to remind Hashem that even though we have just sinned and are deservant of death and destruction, He has made a promise to our forefathers and will therefore not destroy us. The Torah later says that the Tzitz that is worn on the Kohein Godol's head is for atonement (שמות שם פסוק ל"ח) When one looks at someone, he usually looks at the face first and then gets a glimpse of the shoulders. Hashem, when looking at the Kohein Godol, would first notice the Tzitz, which symbolizes forgiveness, but if He decides not to forgive us, then the second thing Hashem would notice would be the stones on his shoulders which symbolize the Bris that Hashem made and will not break.
At the same time, though, the stones may serve as a remembrance for us too. When Yaakov woke up, he said "Hashem is in this place and I didn't know it" (בראשית שם פסוק ט"ז). This idea should remind Bnai Yisrael later that when they sin, they think that Hashem isn't really there; the stones, though, will remind Bnai Yisrael that Hashem is always there, whether everyone knows and realize it or not. The stones remind Bnai Yisrael that Hashem is watching, and that there is always punishment for bad deeds and reward for good ones, and that Hashem will always keep His promises.
It is interesting that when Yaakov awoke, there was only one stone under his head. A little later, Yaakov removes a stone from on top of a well (בראשית כ"ט:י'). Perhaps the one stone under Yaakov's head when he woke up symbolizes the relationship between man and Hashem, while the one stone on the well symbolizes the relationship between man and man. The Luchos, however, were made of two stones, similar to the two stones on the Kohein Gadol's shoulders; these stones perhaps represent both relationships. The Kohein Godol, carrying the names of Bnai Yisrael and representing the Beis HaMikdash, is the unifying force, connecting all of Bnai Yisrael and all of the Mitzvos with Hashem and His promise to Yaakov about us, his descendants.