Claim. Siblings of all four kinds — elder brother, elder sister, younger brother, younger sister — are needed for a complete family because they create the horizontal four directions; sibling love is what makes the family three-dimensional and expands outward into nation, world, and Kingdom.
Elaboration. SMM gives siblings a cosmological function: “If they don’t have siblings of all kinds, they are unhappy. God protects the family in which the younger brother and sister and the elder brother and sister are all present and completely one… The elder brother and elder sister represent the east and west; the younger brother and younger sister represent the north and south. When these become perfected, they become three-dimensional. This is the law of love. When this law of love is established, the origin of peace is created” (Section 7. Love between Siblings If parents have only one son or daugh- ter, what happens? The son needs an elder sister and an elder brother, does he not? The daughter needs an elder brother and an elder sister. They also need a younger brother and sister. If they don’t have sib- lings of all kinds, they are unhappy. God protects the family in which the younger brother and sister and the elder brother and sister are all present and completely one. This becomes the foundation for a, 20-40, 1968.3.31). Sibling love can outrank even parental love: “The person who is willing to love his brother even more than he does his parents will live eternally in heaven” (ibid, 78-41, 1975.5.1). Siblings teach the highest, quickest path to Heaven because they are partners “in the same kind of love” (ibid, 106-80, 1979.12.9). When siblings expand, they “create this sphere… they become citizens of a nation. Brotherly love leads to love toward the world” (ibid, 235-268, 1992.10.11). The family is therefore the geometric model from which world peace must derive.
See also. four-position-foundation