The Kitáb-i-Aqdas
Notes
194.We have appointed two signs for the coming of age of the human race   ¶189
The first sign of the coming of age of humanity referred to in the Writings of Bahá’u’lláh is the emergence of a science which is described as that “divine philosophy” which will include the discovery of a radical approach to the transmutation of elements. This is an indication of the splendours of the future stupendous expansion of knowledge.
Concerning the “second” sign which Bahá’u’lláh indicates to have been revealed in the Kitáb-i-Aqdas, Shoghi Effendi states that Bahá’u’lláh, “…in His Most Holy Book, has enjoined the selection of a single language and the adoption of a common script for all on earth to use, an injunction which, when carried out, would, as He Himself affirms in that Book, be one of the signs of the ‘coming of age of the human race.’”1
Further insight into this process of mankind’s coming of age and proceeding to maturity is provided by the following statement of Bahá’u’lláh:
One of the signs of the maturity of the world is that no one will accept to bear the weight of kingship. Kingship will remain with none willing to bear alone its weight. That day will be the day whereon wisdom will be manifested among mankind.2
The coming of age of the human race has been associated by Shoghi Effendi with the unification of the whole of mankind, the establishment of a world commonwealth, and an unprecedented stimulus to “the intellectual, the moral and spiritual life of the entire human race.”
 
1 Shoghi Effendi, God Passes By,   p. 211
2 Shoghi Effendi, The Promised Day is Come,   pp. 70-71