From the Writings of `Abdu’l-Baha:
And among the teachings of Baha’u’llah is that religious, racial, political, economic and patriotic prejudices destroy the edifice of humanity. As long as these prejudices prevail, the world of humanity will not have rest. For a period of 6,000 years history informs us about the world of humanity. During these 6,000 years the world of humanity has not been free from war, strife, murder and bloodthirstiness. In every period war has been waged in one country or another and that war was due to either religious prejudice, racial prejudice, political prejudice or patriotic prejudice. It has therefore been ascertained and proved that all prejudices are destructive of the human edifice. As long as these prejudices persist, the struggle for existence must remain dominant, and bloodthirstiness and rapacity continue. Therefore, even as was the case in the past, the world of humanity cannot be saved from the darkness of nature and cannot attain illumination except through the abandonment of prejudices and the acquisition of the morals of the Kingdom.
(`Abdu’l-Baha: Selections … `Abdu’l-Baha, p. 299)

And the breeding-ground of all these tragedies is prejudice: prejudice of race and nation, of religion, of political opinion; and the root cause of prejudice is blind imitation of the past – imitation in religion, in racial attitudes, in national bias, in politics. So long as this aping of the past persisteth, just so long will the foundations of the social order be blown to the four winds, just so long will humanity be continually exposed to direst peril.
(`Abdu’l-Baha: Selections … `Abdu’l-Baha, p. 247)

From the Utterances of `Abdu’l-Baha:
According to the teachings of Baha’u’llah all religious, racial, patriotic and political prejudice must be abandoned, for these are the destroyers of the real foundation of humanity.
(`Abdu’l-Baha: Promulgation of Universal Peace, p. 299)

Therefore, religious prejudice is especially opposed to the will and command of God. Racial and national prejudices which separate mankind into groups and branches, likewise, have a false and unjustifiable foundation, for all men are the children of Adam and essentially of one family. There should be no racial alienation or national division among humankind. Such distinctions as French, German, Persian, Anglo-Saxon are human and artificial; they have neither significance nor recognition in the estimation of God. In His estimate all are one, the children of one family; and God is equally kind to them. The earth has one surface. God has not divided this surface by boundaries and barriers to separate races and peoples. Man has set up and established these imaginary lines, giving to each restricted area a name and the limitation of a native land or nationhood. By this division and separation into groups and branches of mankind, prejudice is engendered which becomes a fruitful source of war and strife. Impelled by this prejudice, races and nations declare war against each other; the blood of the innocent is poured out, and the earth torn by violence. Therefore, it has been decreed by God in this day that these prejudices and differences shall be laid aside.
(`Abdu’l-Baha: Promulgation of Universal Peace, p. 316)

If we harbor prejudice, it will be the cause of deprivation and ignorance. The strife between religions, nations and races arises from misunderstanding. If we investigate the religions to discover the principles underlying their foundations, we will find they agree; for the fundamental reality of them is one and not multiple. By this means the religionists of the world will reach their point of unity and reconciliation. They will ascertain the truth that the purpose of religion is the acquisition of praiseworthy virtues, the betterment of morals, the spiritual development of mankind, the real life and divine bestowals.
(`Abdu’l-Baha: Promulgation of Universal Peace, p. 152)

One of the forms of prejudice which afflict the world of mankind is religious bigotry and fanaticism. When this hatred burns in human hearts, it becomes the cause of revolution, destruction, abasement of humankind and deprivation of the mercy of God. For the holy Manifestations and divine Founders of religion Themselves were completely unified in love and agreement, whereas Their followers are characterized by bitter antagonism and attitudes of hostility toward each other. God has desired for mankind the effulgence of love, but through blindness and misapprehension man has enveloped himself in veils of discord, strife and hatred.
(`Abdu’l-Baha: Promulgation of Universal Peace, pp. 337-338)

Blessed souls – whether Moses, Jesus, Zoroaster, Krishna, Buddha, Confucius or Muhammad – were the cause of the illumination of the world of humanity. How can we deny such irrefutable proof? How can we be blind to such light? How can we dispute the validity of Christ? This is injustice. This is a denial of reality. Man must be just. We must set aside bias and prejudice. We must abandon the imitations of ancestors and forefathers. We ourselves must investigate reality and be fair in judgment.
(`Abdu’l-Baha: Promulgation of Universal Peace, p. 346)

Other wars are caused by purely imaginary racial differences; for humanity is one kind, one race and progeny, inhabiting the same globe. In the creative plan there is no racial distinction and separation such as Frenchman, Englishman, American, German, Italian or Spaniard; all belong to one household. These boundaries and distinctions are human and artificial, not natural and original. All mankind are the fruits of one tree, flowers of the same garden, waves of one sea.
(`Abdu’l-Baha: Promulgation of Universal Peace, p. 118)

God maketh no distinction between the white and the black. If the hearts are pure both are acceptable unto Him. God is no respecter of persons on account of either color or race. All colors are acceptable to Him, be they white, black, or yellow. Inasmuch as all were created in the image of God, we must bring ourselves to realize that all embody divine possibilities.
(`Abdu’l-Baha: Promulgation of Universal Peace, p. 113)

Therefore, be it known that color or race is of no importance. He who is the image and likeness of God, who is the manifestation of the bestowals of God, is acceptable at the threshold of God – whether his color be white, black or brown; it matters not. Man is not man simply because of bodily attributes. The standard of divine measure and judgment is his intelligence and spirit.
(`Abdu’l-Baha: Promulgation of Universal Peace, p. 70)

In order to find truth we must give up our prejudices, our own small trivial notions; an open receptive mind is essential. If our chalice is full of self, there is no room in it for the water of life. The fact that we imagine ourselves to be right and everybody else wrong is the greatest of all obstacles in the path towards unity, and unity is necessary if we would reach truth, for truth is one.
Therefore it is imperative that we should renounce our own particular prejudices and superstitions if we earnestly desire to seek the truth. Unless we make a distinction in our minds between dogma, superstition and prejudice on the one hand, and truth on the other, we cannot succeed.
(`Abdu’l-Baha: Paris Talks, p. 136)

You must be free from prejudice and fanaticism, beholding no differences between the races and religions. You must look to God, for He is the real Shepherd, and all humanity are His sheep. He loves them and loves them equally.
(`Abdu’l-Baha: Promulgation of Universal Peace, pp. 468-469)

Be kind to all people, love humanity, consider all mankind as your relations and servants of the most high God. Strive day and night that animosity and contention may pass away from the hearts of men, that all religions shall become reconciled and the nations love each other so that no racial, religious or political prejudice may remain and the world of humanity behold God as the beginning and end of all existence. God has created all, and all return to God. Therefore, love humanity with all your heart and soul.
(`Abdu’l-Baha: Promulgation of Universal Peace, p. 291)

Behold a beautiful garden full of flowers, shrubs, and trees. Each flower has a different charm, a peculiar beauty, its own delicious perfume and beautiful colour. The trees too, how varied are they in size, in growth, in foliage – and what different fruits they bear! Yet all these flowers, shrubs and trees spring from the self-same earth, the same sun shines upon them and the same clouds give them rain.
So it is with humanity. It is made up of many races, and its peoples are of different colour, white, black, yellow, brown and red – but they all come from the same God, and all are servants to Him. This diversity among the children of men has unhappily not the same effect as it has among the vegetable creation, where the spirit shown is more harmonious. Among men exists the diversity of animosity, and it is this that causes war and hatred among the different nations of the world.
Differences which are only those of blood also cause them to destroy and kill one another. Alas! that this should still be so. Let us look rather at the beauty in diversity, the beauty of harmony, and learn a lesson from the vegetable creation. If you beheld a garden in which all the plants were the same as to form, colour and perfume, it would not seem beautiful to you at all, but, rather, monotonous and dull. The garden which is pleasing to the eye and which makes the heart glad, is the garden in which are growing side by side flowers of every hue, form and perfume, and the joyous contrast of colour is what makes for charm and beauty. So is it with trees. An orchard full of fruit trees is a delight; so is a plantation planted with many species of shrubs. It is just the diversity and variety that constitutes its charm; each flower, each tree, each fruit, beside being beautiful in itself, brings out by contrast the qualities of the others, and shows to advantage the special loveliness of each and all.
Thus should it be among the children of men! The diversity in the human family should be the cause of love and harmony, as it is in music where many different notes blend together in the making of a perfect chord. If you meet those of different race and colour from yourself, do not mistrust them and withdraw yourself into your shell of conventionality, but rather be glad and show them kindness. Think of them as different coloured roses growing in the beautiful garden of humanity, and rejoice to be among them.
Likewise, when you meet those whose opinions differ from your own, do not turn away your face from them. All are seeking truth, and there are many roads leading thereto. Truth has many aspects, but it remains always and forever one.
Do not allow difference of opinion, or diversity of thought to separate you from your fellow-men, or to be the cause of dispute, hatred and strife in your hearts.
Rather, search diligently for the truth and make all men your friends.
Every edifice is made of many different stones, yet each depends on the other to such an extent that if one were displaced the whole building would suffer; if one is faulty the structure is imperfect.
Baha’u’llah has drawn the circle of unity, He has made a design for the uniting of all the peoples, and for the gathering of them all under the shelter of the tent of universal unity. This is the work of the Divine Bounty, and we must all strive with heart and soul until we have the reality of unity in our midst, and as we work, so will strength be given unto us. Leave all thought of self, and strive only to be obedient and submissive to the Will of God. In this way only shall we become citizens of the Kingdom of God, and attain unto life everlasting.
(`Abdu’l-Baha: Paris Talks, pp. 52-54)

The age has dawned when human fellowship will become a reality.
The century has come when all religions shall be unified.
The dispensation is at hand when all nations shall enjoy the blessings of international peace.
The cycle has arrived when racial prejudice will be abandoned by tribes and peoples of the world.
The epoch has begun wherein all native lands will be conjoined in one great human family.
For all mankind shall dwell in peace and security beneath the shelter of the great tabernacle of the one living God.
(`Abdu’l-Baha: Promulgation of Universal Peace, p. 370)