The Twelve Stones
The beginning of the Torah portion described Yaakov's departure from Be'er Sheva and his famous dream of the ladder. Before he lay down to sleep, we learn:
He took some of the stones from the place, and he set it under his head... (Bereishis 28:11)
But after he had dreamed and awoken, we discover:
He took the stone which he had set under his head and erected it as a monument... (Ibid., 18)
The Midrash notes the discrepancy between the two verses (was it one or many stones?) and assumes that the many stones actually became one:
Rabbi Yehudah said: "He took 12 stones, as God had decreed that he would establish 12 tribes. Yaakov said, 'Avraham didn't establish them. Yitzchak didn't establish them. As for me, if the 12 stones become one, then I will know that I will establish 12 tribes.' When the 12 stones became one, he knew that he would establish 12 tribes." (Bereishis Rabbah 68:11)
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PRESERVING AND DESTROYING UNITY
To begin to understand this, let us consider one aspect of unity: how it is destroyed. My holy father said that it is a fundamental principle of unity that if one adds something to a complete set, not only does the set have an alien member, but it is spoiled entirely. For example, our Sages indicate that if one needs to bind together the arba minim, the Four Species we wave on Sukkot, we can assume that the tied bundle forms a discrete entity. If so, the addition of an extra item, for example, a banana, will completely ruin the nature of the bundle. It will not be arba minim plus a banana, but rather nothing of value at all.
We may apply this principle to the nature of the 12 tribes. The Torah tells us:
And there was a king in Yeshurun when the heads of the people gathered the tribes of Yisrael together. (Devarim 33:5)
The Torah here describes Klal Yisrael as a united entity - a perfect and complete national body. Adding to it or subtracting from it will spoil its uniqueness and beauty. Together, working in harmony, Yisrael is a world unto itself, pulsating with the vibrancy of unity. Indeed, the number twelve is used to indicate completeness on a grand scale: there are twelve zodiac signs, twelve months of the year, and, to correspond, twelve tribes of Yisrael. If there were some interference or attempt at adding to the heavenly array, a disaster of cosmic proportions would ensue. So too, if any addition or subtraction were to befall Klal Yisrael, then its very purpose would be frustrated.
Klal Yisrael comprises many different people, each with their own distinct personality. How, then, is this prized unity to be achieved and maintained? Each member of the nation must subjugate his own needs and desires to those of God. In this way alone can true unity be achieved, enabling the klal to function as one organism with a single overall purpose.
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YAAKOV: FOUNDER OF KLAL YISRAEL
Perhaps we can suggest why Avraham and Yitzchak were unable to be the direct progenitors of the twelve tribes and of Klal Yisrael. Avraham produced Yishmael, and Yitzchak produced Eisav, each of whom could not continue in his father's footsteps. But in addition, each produced a son who did continue the link, namely Yitzchak and Yaakov. But this meant that both Avraham and Yitzchak had fathered a set of two children, one good and one bad. There could be no unity in either group, for as we have seen, the existence of an alien entity within the group spoils its very nature. There was, in fact, no purpose in them having more than one good son, for once there was no possibility of creating the unified set which comprises Klal Yisrael, then further offspring could achieve nothing. Unity, we have said, is a prerequisite for proper Jewish existence, and certainly a requirement ab initio for the establishment of Klal Yisrael. Therefore, neither Avraham nor Yitzchak had a chance of establishing the twelve tribes. That required an entirely different person: Yaakov, our Forefather.
When Yaakov left his parental home to find a wife and to fulfill his life's mission, he wanted to know whether or not he would be blessed with success. So when he lay down to sleep, he performed the test described in the midrash above. The unification of the stones would indicate to him whether he, in contrast to his father and grandfather, would become the progenitor of Klal Yisrael. Unity, as we have mentioned, points to subjugation of the individual's needs to that of the klal. Yaakov knew that if the stones joined together, then this would symbolize that he would father the tribes - tzaddikim who could unify, without any division or alien intrusion, and form the basis of Klal Yisrael.