September 7

…as the basis for distinction is in the person's capacity and ability, and differences are related to the degree of his intelligence and mental powers, therefore, all the people will not be equal in their knowledge, learning and understanding. The intent is to say that the world of creation calls for distinctions in people's stations, and degrees in the differences existing among them, so that the affairs of the world may become organized and ordered. Diversity in all created things, whether in kind, in physical appearance, or in station, is the means for their protection, their permanence, unity and harmony. Each part complements the other. 
(From a letter dated 22 May 1928 written on behalf of Shoghi Effendi to an individual believer, translated from Persian;The Compilation of Compilations, vol. III, Economics, Agriculture, and Related Subjects)