Humanity is One Family:
The earth is but one country, and mankind its citizens.
(Baha’u’llah: Gleanings, p. 250)

Ye are the fruits of one tree, and the leaves of one branch. Deal ye one with another with the utmost love and harmony, with friendliness and fellowship.
(Baha’u’llah: Gleanings, p. 288)

Baha’u’llah has addressed the world of humanity, saying, “Verily, ye are the fruits of one tree and the leaves of one branch.” This signifies that the entire world of humanity is one tree. The various nations and peoples are the branches of that tree. Individual members of mankind are represented by the twigs and blossoms.
(`Abdu’l-Baha: Promulgation of Universal Peace, p. 373)

A fundamental teaching of Baha’u’llah 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.” By this it is meant that the world of humanity is like a tree, the nations or peoples are the different limbs or branches of that tree, and the individual human creatures are as the fruits and blossoms thereof. In this way Baha’u’llah expressed the oneness of humankind, whereas in all religious teachings of the past the human world has been represented as divided into two parts: one known as the people of the Book of God, or the pure tree, and the other the people of infidelity and error, or the evil tree. The former were considered as belonging to the faithful, and the others to the hosts of the irreligious and infidel – one part of humanity the recipients of divine mercy, and the other the object of the wrath of their Creator. Baha’u’llah removed this by proclaiming the oneness of the world of humanity, and this principle is specialized in His teachings, for He has submerged all mankind in the sea of divine generosity.
(`Abdu’l-Baha: Promulgation of Universal Peace, p. 454)

Baha’u’llah taught the Oneness of humanity; that is to say, all the children of men are under the mercy of the Great God. They are the sons of one God; they are trained by God. He has placed the crown of humanity on the head of every one of the servants of God. Therefore all nations and peoples must consider themselves brethren. They are all descendants from Adam. They are the branches, leaves, flowers and fruits of One Tree.
(`Abdu’l-Baha: Abdu’l-Baha in London, p. 28)

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. In the animal kingdom no such distinction and separation are observed.
(`Abdu’l-Baha: Promulgation of Universal Peace, p. 118)

With reference to your question as to the meaning of the passage of `he who loves his kind’, the statement of Baha’u’llah does not refer to any special race or class of people. Rather it includes the entire human race, irrespective of any class, creed or colour. The Message of Baha’u’llah is not a particularistic appeal to a group of people. It is a Universal Message and all-inclusive appeal. His principle of the oneness of mankind is world-wide in its spirit, in its application, and covers the entire field of human relationships.
(Shoghi Effendi: Lights of Guidance, p. 481)

Duty to Unite the Human Race:
It is incumbent upon all the peoples of the world to reconcile their differences, and, with perfect unity and peace, abide beneath the shadow of the Tree of His care and loving-kindness.
(Baha’u’llah: Gleanings, p. 6)

O contending peoples and kindreds of the earth! Set your faces towards unity, and let the radiance of its light shine upon you. Gather ye together, and for the sake of God resolve to root out whatever is the source of contention amongst you. Then will the effulgence of the world’s great Luminary envelop the whole earth, and its inhabitants become the citizens of one city, and the occupants of one and the same throne.
(Baha’u’llah: Gleanings, p. 217)

O CHILDREN OF MEN! Know ye not why We [God] created you all from the same dust? That no one should exalt himself over the other. Ponder at all times in your hearts how ye were created. Since We have created you all from one same substance it is incumbent on you to be even as one soul, to walk with the same feet, eat with the same mouth and dwell in the same land, that from your inmost being, by your deeds and actions, the signs of oneness and the essence of detachment may be made manifest. Such is My counsel to you, O concourse of light! Heed ye this counsel that ye may obtain the fruit of holiness from the tree of wondrous glory.
(Baha’u’llah: Arabic Hidden Words, p. 68)

We must use these powers in establishing the oneness of the world of humanity, appreciate these virtues by accomplishing the unity of whites and blacks, devote this divine intelligence to the perfecting of amity and accord among all branches of the human family so that under the protection and providence of God the East and West may hold each other’s hands and become as lovers. Then will mankind be as one nation, one race and kind – as waves of one ocean.
(`Abdu’l-Baha: Promulgation of Universal Peace, p. 51)

The Baha’i Faith Unites Humanity:
The fundamental purpose animating the Faith of God and His Religion is to safeguard the interests and promote the unity of the human race, and to foster the spirit of love and fellowship amongst men.
(Baha’u’llah: Gleanings, p. 215)

The well-being of mankind, its peace and security, are unattainable unless and until its unity is firmly established. This unity can never be achieved so long as the counsels which the Pen of the Most High hath revealed are suffered to pass unheeded.
Through the power of the words He hath uttered the whole of the human race can be illumined with the light of unity, and the remembrance of His Name is able to set on fire the hearts of all men, and burn away the veils that intervene between them and His glory.
(Baha’u’llah: Gleanings, pp. 286-287)

Of the principles enshrined in these Tablets the most vital of them all is the principle of the oneness and wholeness of the human race, which may well be regarded as the hall-mark of Baha’u’llah’s Revelation and the pivot of His teachings. Of such cardinal importance is this principle of unity that it is expressly referred to in the Book of His Covenant, and He unreservedly proclaims it as the central purpose of His Faith.
(Shoghi Effendi: God Passes By, pp. 216-217)

The principle of the Oneness of Mankind – the pivot round which all the teachings of Baha’u’llah revolve – is no mere outburst of ignorant emotionalism or an expression of vague and pious hope. Its appeal is not to be merely identified with a reawakening of the spirit of brotherhood and good-will among men, nor does it aim solely at the fostering of harmonious cooperation among individual peoples and nations. Its implications are deeper, its claims greater than any which the Prophets of old were allowed to advance. Its message is applicable not only to the individual, but concerns itself primarily with the nature of those essential relationships that must bind all the states and nations as members of one human family. It does not constitute merely the enunciation of an ideal, but stands inseparably associated with an institution adequate to embody its truth, demonstrate its validity, and perpetuate its influence. It implies an organic change in the structure of present-day society, a change such as the world has not yet experienced. It constitutes a challenge, at once bold and universal, to outworn shibboleths of national creeds – creeds that have had their day and which must, in the ordinary course of events as shaped and controlled by Providence, give way to a new gospel, fundamentally different from, and infinitely superior to, what the world has already conceived. It calls for no less than the reconstruction and the demilitarization of the whole civilized world – a world organically unified in all the essential aspects of its life, its political machinery, its spiritual aspiration, its trade and finance, its script and language, and yet infinite in the diversity of the national characteristics of its federated units.
It represents the consummation of human evolution – an evolution that has had its earliest beginnings in the birth of family life, its subsequent development in the achievement of tribal solidarity, leading in turn to the constitution of the city-state, and expanding later into the institution of independent and sovereign nations.
The principle of the Oneness of Mankind, as proclaimed by Baha’u’llah, carries with it no more and no less than a solemn assertion that attainment to this final stage in this stupendous evolution is not only necessary but inevitable, that its realization is fast approaching, and that nothing short of a power that is born of God can succeed in establishing it.
(Shoghi Effendi: World Order of Baha’u’llah, pp. 42-43)

Guidelines for Uniting Humanity:
Let not a man glory in this, that he loves his country; let him rather glory in this, that he loves his kind….
(Baha’u’llah: Peace, p. 157)

Address yourselves to the promotion of the well-being and tranquillity of the children of men. Bend your minds and wills to the education of the peoples and kindreds of the earth, that haply the dissensions that divide it may, through the power of the Most Great Name, be blotted out from its face, and all mankind become the upholders of one Order, and the inhabitants of one City. Illumine and hallow your hearts; let them not be profaned by the thorns of hate or the thistles of malice. Ye dwell in one world, and have been created through the operation of one Will. Blessed is he who mingleth with all men in a spirit of utmost kindliness and love.
(Baha’u’llah: Gleanings, pp. 333-334)

“Consort with the followers of all religions in a spirit of friendliness and fellowship.” Whatsoever hath led the children of men to shun one another, and hath caused dissensions and divisions amongst them, hath, through the revelation of these words, been nullified and abolished.
(Baha’u’llah: Gleanings, p. 95)

The day is approaching when all the peoples of the world will have adopted one universal language and one common script. When this is achieved, to whatsoever city a man may journey, it shall be as if he were entering his own home. These things are obligatory and absolutely essential. It is incumbent upon every man of insight and understanding to strive to translate that which hath been written into reality and action…. That one indeed is a man who, today, dedicateth himself to the service of the entire human race. The Great Being saith: Blessed and happy is he that ariseth to promote the best interests of the peoples and kindreds of the earth. In another passage He hath proclaimed: It is not for him to pride himself who loveth his own country, but rather for him who loveth the whole world.
(Baha’u’llah: Gleanings, pp. 249-250)

Beware lest the desires of the flesh and of a corrupt inclination provoke divisions among you. Be ye as the fingers of one hand, the members of one body. Thus counselleth you the Pen of Revelation, if ye be of them that believe.
(Baha’u’llah: The Kitab-i-Aqdas, p. 40)

O people of Justice! Be as brilliant as the light, and as splendid as the fire that blazed in the Burning Bush. The brightness of the fire of your love will no doubt fuse and unify the contending peoples and kindreds of the earth, whilst the fierceness of the flame of enmity and hatred cannot but result in strife and ruin.
(Baha’u’llah: Gleanings, p. 96)

O humankind! Verily, ye are all the leaves and fruits of one tree; ye are all one. Therefore, associate in friendship; love one another; abandon prejudices of race; dispel forever this gloomy darkness of human ignorance, for the century of light, the Sun of Reality hath appeared. Now is the time for affiliation, and now is the period of unity and concord. For thousands of years ye have been contending in warfare and strife. It is enough. Now is the time for unity. Lay aside all self-purposes, and know for a certainty that all men are the servants of one God Who will bind them together in love and agreement.
(`Abdu’l-Baha: Promulgation of Universal Peace, p. 322)

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)