Oneness of God and unity of mankind.

The great and fundamental teachings of Bahá’u’lláh are the oneness of God and unity of mankind. This is the bond of union among Bahá’ís all over the world. They become united among themselves, then unite others. It is impossible to unite unless united. Christ said, “Ye are the salt of the earth; but if the salt has lost his savour, wherewith shall it be salted?” This proves there were dissensions and lack of unity among His followers. Hence His admonition to unity of action.
Now must we, likewise, bind ourselves together in the utmost unity, be kind and loving to each other, sacrificing all our possessions, our honor, yea, even our lives for each other. Then will it be proved that we have acted according to the teachings of God, that we have been real believers in the oneness of God and unity of mankind.

`Abdu'l-Bahá: The Promulgation of Universal Peace