From Abdul Baha'

"The world of humanity is one and God is equally kind to all. What then is the source of unkindness and hatred in the human world? This real shepherd loves all his sheep. He leads them in green pastures. He rears and protects them. What then is the source of enmity and alienation among humankind? Whence this conflict and strife? The real underlying cause is lack of religious unity and association for in each of the great religions we find superstition, blind imitation of creeds, and theological formulae adhered to instead of the divine fundamentals, causing difference and divergence among mankind instead of agreement and fellowship. Consequently strife, hatred and warfare have arisen, based upon this divergence and separation. If we investigate the foundations of the divine religions, we find them to be one, absolutely changeless and never subject to transformation. For example each of the divine religions contains two kinds of laws or ordinances. One division concerns the world of morality and ethical institutions. These are the essential ordinances. They instill and awaken the knowledge and love of God, love for humanity, the virtues of the world of mankind, the attributes of the divine kingdom, rebirth and resurrection from the kingdom of nature. These constitute one kind of divine law which is common to all and never subject to change. From the dawn of the Adamic cycle to the present day this fundamental law of God has continued changeless. This is the foundation of divine religion.

The second division comprises laws and institutions which provide for human needs and conditions according to exigencies of time and place. These are accidental, of no essential importance and should never have been made the cause and source of human contention. For example during the time of His Holiness Moses—Upon him be peace! —according to the exigencies of that period, divorce was permissible. During the cycle of His Holiness Christ inasmuch as divorce was not in conformity with the time and conditions His Holiness Jesus Christ abrogated it. In the cycle of Moses plurality of wives was permissible but during the time of His Holiness Christ the exigency which had sanctioned it did not exist, therefore it was forbidden. His Holiness Moses lived in the wilderness and desert of Sinai; therefore his ordinances and commandments were in conformity with those conditions. The penalty for theft was to cut off a man’s hand. An ordinance of this kind was in keeping with desert life but not compatible with conditions of the present day. Such ordinances therefore constitute the second or non-essential division of the divine religions and are not of importance for they deal with human transactions which are ever changing according to the requirements of time and place. Therefore the intrinsic foundations of the divine religions are one. As this is true, why should hostility and strife exist among them? Why should this hatred and warfare, ferocity and bloodshed continue? Is this allowable and justified? God forbid!"