He [‘Abdu’l-Baha] alone had been accorded the privilege of
being called "the Master," an honor from which His Father had
strictly excluded all His other sons. Upon Him that loving and unerring Father
had chosen to confer the unique title of "Sirru'llah" (the Mystery of
God), a designation so appropriate to One Who, though essentially human and
holding a station radically and fundamentally different from that occupied by
Bahá'u'lláh and His Forerunner, could still claim to be the perfect Exemplar of
His Faith, to be endowed with super-human knowledge, and to be regarded as the
stainless mirror reflecting His light.
-Shoghi Effendi (God Passes By)
