"Abraham, Moses, Zoroaster, Buddha, Jesus, Muḥammad, the Báb and Bahá’u’lláh are one in spirit..."

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"The holy Manifestations Who have been the Sources or Founders of the various religious systems were united and agreed in purpose and teaching. Abraham, Moses, Zoroaster, Buddha, Jesus, Muḥammad, the Báb and Bahá’u’lláh are one in spirit and reality. Moreover, each Prophet fulfilled the promise of the One Who came before Him and, likewise, Each announced the One Who would follow. Consider how Abraham foretold the coming of Moses, and Moses embodied the Abrahamic statement. Moses prophesied the Messianic cycle, and Christ fulfilled the law of Moses. It is evident, therefore, that the Holy Manifestations Who founded the religious systems are united and agreed; there is no differentiation possible in Their mission and teachings; all are reflectors of reality, and all are promulgators of the religion of God.

The divine religion is reality, and reality is not multiple; it is one. Therefore, the foundations of the religious systems are one because all proceed from the indivisible reality; but the followers of these systems have disagreed; discord, strife and warfare have arisen among them, for they have forsaken the foundation and held to that which is but imitation and semblance. Inasmuch as imitations differ, enmity and dissension have resulted. For example, Jesus Christ—may my spirit be a sacrifice unto Him!—laid the foundation of eternal reality, but after His departure many sects and divisions appeared in Christianity. What was the cause of this? There is no doubt that they originated in dogmatic imitations, for the foundations of Christ were reality itself, in which no divergence exists. When imitations appeared, sects and denominations were formed."

-`Abdu'l-Bahá, The Promulgation of Universal Peace, p. 197
16 June 1912 Talk at Central Congregational Church, Hancock Street, Brooklyn, New York