In a letter addressed to Queen Victoria over a century ago, and employing an analogy that points to the one model holding convincing promise for the organization of a planetary society, Bahá'u'lláh compared the world to the human body. There is, indeed, no other model in phenomenal existence to which we can reasonably look. Human society is composed not of a mass of merely differentiated cells but of associations of individuals, each one of whom is endowed with intelligence and will; nevertheless, the modes of operation that characterize man's biological nature illustrate fundamental principles of existence. Chief among these is that of unity in diversity. Paradoxically, it is precisely the wholeness and complexity of the order constituting the human body--and the perfect integration into it of the body's cells--that permit the full realization of the distinctive capacities inherent in each of these component elements. No cell lives apart from the body, whether in contributing to its functioning or in deriving its share from the well-being of the whole. The physical well-being thus achieved finds its purpose in making possible the expression of human consciousness; that is to say, the purpose of biological development transcends the mere existence of the body and its parts.
What is true of the life of the individual has its parallels in human society. The human species is an organic whole, the leading edge of the evolutionary process. That human consciousness necessarily operates through an infinite diversity of individual minds and motivations detracts in no way from its essential unity. Indeed, it is precisely an inhering diversity that distinguishes unity from homogeneity or uniformity. What the peoples of the world are today experiencing, Bahá'u'lláh said, is their collective coming- of-age, and it is through this emerging maturity of the race that the principle of unity in diversity will find full expression. From its earliest beginnings in the consolidation of family life, the process of social organization has successively moved from the simple structures of clan and tribe, through multitudinous forms of urban society, to the eventual emergence of the nation-state, each stage opening up a wealth of new opportunities for the exercise of human capacity.