A fundamental teaching of Bahá'u'lláh is the oneness of the world of humanity. Addressing mankind He says: "Ye are all leaves of one tree and the fruits of one branch."
"..In the eyes of the Creator all His children are equal; His goodness is poured forth on all. He does not favor this nation nor that nation, all alike are His creatures. This being so, why should we make divisions, separating one race from another? Why should we create barriers of superstition and tradition bringing discord and hatred among the people?
The only difference between members of the human family is that of degree. Some are like children who are ignorant, and must be educated until they arrive at maturity. Some are like the sick and must be treated with tenderness and care. None are bad or evil! We must not be repelled by these poor children. We must treat them with great kindness, teaching the ignorant and tenderly nursing the sick.
Consider: Unity is necessary to existence. Love is the very cause of life; on the other hand, separation brings death. In the world of material creation, for instance, all things owe their actual life to unity. The elements which compose wood, mineral, or stone, are held together by the law of attraction. If this law should cease for one moment to operate these elements would not hold together, they would fall apart, and the object would in that particular form cease to exist. The law of attraction has brought together certain elements in the form of this beautiful flower, but when that attraction is withdrawn from this centre the flower will decompose, and, as a flower, cease to exist.
So it is with the great body of humanity. The wonderful Law of Attraction, Harmony and Unity, holds together this marvelous Creation.
As with the whole, so with the parts; whether a flower or a human body, when the attracting principle is withdrawn from it, the flower or the man dies. It is therefore clear that attraction, harmony, unity and Love, are the cause of life, whereas repulsion, discord, hatred and separation bring death.
We have seen that whatever brings division into the world of existence causes death. Likewise in the world of the spirit does the same law operate.
Therefore should every servant of the One God be obedient to the law of love, avoiding all hatred, discord, and strife. We find when we observe nature, that the gentler animals group themselves together into flocks and herds, whereas the savage, ferocious creatures, such as the lion, the tiger, and the wolf, live in wild forests, apart from civilization. Two wolves, or two lions, may live amicably together; but a thousand lambs may share the same fold and a large number of deer can form one herd. Two eagles can dwell in the same place, but a thousand doves can gather into one habitation.
Man should, at least, be numbered among the gentler animals; but when he becomes ferocious he is more cruel and malicious than the most savage of the animal creation!
Now Bahá'u'lláh has proclaimed the 'Unity of the World of Mankind'. All peoples and nations are of one family, the children of one Father, and should be to one another as brothers and sisters! I hope that you will endeavour in your lives to show forth and spread this teaching.
Bahá'u'lláh said that we should love even our enemies and be to them as friends. If all men were obedient to this principle, the greatest unity and understanding would be established in the hearts of mankind."
('Abdu'l-Bahá: Paris Talks, Pages: 138-140)