Some Ans. Questions 1908 by -'Abdu'l-Bahá- 1 Para

In each cycle the guardians and holy souls have been twelve. So Jacob had twelve sons; in the time of Moses there were twelve heads or chiefs of the tribes; in the time of Christ there were twelve Apostles; and in the time of Muhammad there were twelve Imams. But in this glorious manifestation there are twenty-four, double the number of all the others, for the greatness of this manifestation requires it. These holy souls are in the presence of God seated on their own thrones, meaning that they reign eternally (57:3)

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