The Bahá’í Faith emphasizes the unity of humanity transcending all divisions of race, nation, gender, caste, and social class, while celebrating its diversity. Bahá’u’lláh wrote: "The earth is but one country, and mankind its citizens." ‘Abdu’l-Bahá adds that the "unification of mankind" has now become "the paramount issue and question in the religious and political conditions of the world." The Bahá’í writings affirm the biological, political, and spiritual unity of humankind, while noting that they are not necessarily expected to arise simultaneously. "The world of existence is like unto an orchard and humanity is like unto the trees. All these trees are planted in the same orchard, reared through the heat of one sun, watered with one rain. We must be the cause of the adornment of this orchard. The world of humanity is like unto a rose garden and the various races, tongues and people are like unto contrasting flowers. The diversity of colors in a rose-garden adds to the charm and beauty of the scene as variety enhances unity." -‘Abdu’l-Bahá, Divine Philosophy