The One Law, Cause, or Religion of God

God’s One Religion is also called His Law, Cause, or Supreme Constitution. It has spiritual and material parts. Its spiritual part
is the fundamental basis which comprises all spiritual virtues and divine qualities; this does not change nor alter: it is the Holy of Holies, which is the essence of the Law of Adam, Noah, Abraham, Moses, Christ, Muhammad, the Báb, and Baha’u’llah, and which lasts and is established in all the prophetic cycles. It will never be abrogated, for it is spiritual and not material truth; it is faith, knowledge, certitude, justice, piety, righteousness, trustworthiness, love of God, benevolence, purity, detachment, humility, meekness, patience and constancy. It shows mercy to the poor, defends the oppressed, gives to the wretched and uplifts the fallen. These divine qualities, these eternal commandments, will never be abolished; nay, they will last and remain established for ever and ever. These virtues of humanity will be renewed in each of the different [Eras]; for at the end of every [Era] the spiritual Law of God...disappears, and only the form subsists. Thus among the Jews…‌the Law of God disappeared...a form without spirit remaining. The Holy of Holies departed....But the outer court…the expression used for the form of the religion—fell into the hands of the Gentiles. In the same way, the fundamental principles of the religion of Christ¼have disappeared; and its form has remained in the hands of the clergy....Likewise, the foundation of the religion of Muhammad has disappeared, but its form remains in the hands of the official ‘ulamá.1]
Each Messenger of God Stressed a Facet of the Central Spiritual Law relevant to his area and Era:
Abraham stressed the idol-free worship of one God
Moses stressed justice
Zoroaster stressed good defeating evil
Krishna stressed the Presence of God in everybody
Buddha stressed personal enlightenment
Jesus stressed brotherly love
Muhammad stressed loving submission to God and social love
The Bab and Baha’u’llah stressed unity.
The Golden Rule to Love God and Treat Others as Oneselfis the bedrock of the spiritual part of the Law of God. In its own words, each Faith teaches it:
Judaism: Love your fellow as yourself. What is hateful to you, do not do to your neighbor. This is the whole Torah.
Zoroastrianism: Nature only is good when it shall not do to another whatever is not good for its own self. Whatever is disagreeable to yourself do not do unto others.
Hinduism: This is the sum of duty: Do naught unto others which would cause you pain if done to you. One should not behave towards others in a way which is disagreeable to oneself. This is the essence of morality.
Buddhism: A clansman should treat his friends and familiars as he treats himself and being as good as his word. Do not hurt others in ways that you yourself would find hurtful.
Christianity: In everything, do to others what you would have them do to you, for this sums up the Law and the Prophets.
Islam: Wish for others what you wish for yourself. None of you is a believer until he desires for his brother that which he desires for himself. Hurt no one so that no one may hurt you.
Baha’i Faith: Choose thou for thy neighbour that which thou choosest for thyself. Wish not for others what you wish not for yourselves. Lay not on any soul a load which ye would not wish to be laid upon you. The seeker should notpromise that which he does not fulfill. He must notspeak that which he would not bear to hear spoken by another, nor yet desire for any soul that which he would not have desired for himself. Blessed is he who prefers his brother before himself.[2]
Then the second part of the Religion of Godrefers to the material world, andcomprises fasting, prayer, forms of worship, marriage and divorce, the abolition of slavery, legal processes, transactions, indemnities for murder, violence, theft and injuries—this part of the Law of God…is modified and altered in each prophetic cycle in accordance with the necessities of the times.[3]

Accordingly, Messengers of God revamp calendars and festivals, material laws about food and marriage, and more. Each Faith celebrates a whole raft of specific festivals on the calendar that defines it, and it alone. As for food, Jews and Muslims avoid pork while Christians eat it. As for marriage, Abraham forbade brother-sister marriage (he had been made to marry his half-sister Sarah); Moses forbade aunt-nephew marriage (his mother was aunt to his father)[4]; and Christianity frowns on cousin marriage. And so on.

[1] ‘Abdu’l-Bahá, SAQ11.47–48
[2] Judaism: Levit. 19.18; Hillel, Babylonian Talmud, Shabbat 31a
 Zoroastrianism: Dadistan-i-Dinik 94:5; Shayast-na-Shayast 13.29
 Hinduism: Mahabharata 5.1517; Anusasana Parva 113.8
 Buddhism: Dhammapada Udana-Varga 5.18
 Christianity: Matt. 7.12
 Islam: Hadith Al-Bukhari 1.38; Hadith An-Nawawi 13.4; MuhammadFarewell Sermon
 Bahá'í Faith:TB6.64; Aqdas 148.73; Summons of the Lord of Hosts 5.44.202; GWB125.265–66; Gems 62;BWF185
[3] ‘Abdu’l-Bahá, SAQ11.47–48
[4] Yet Jewish Law still lets uncles marry nieces; I have seen three babies of such unions, two with major congenital anomalies.