The Prophets and Messengers of God . . . are like unto leaven which leaveneth the world of being, and constitute the animating force through which the arts and wonders of the world are made manifest.

Bahá’u’lláh, Gleanings from the Writings of Bahá’u’lláh, p. 156-157

Those souls that are the symbols of detachment are the leaven of the world. Meditate on this, and be of the thankful.

Bahá’u’lláh, Gleanings from the Writings of Bahá’u’lláh, p. 161

Thou hast, moreover, asked Me concerning the state of the soul after its separation from the body. Know thou, of a truth, that if the soul of man hath walked in the ways of God, it will, assuredly, return and be gathered to the glory of the Beloved . . . Such a soul provideth, at the bidding of the Ideal King and Divine Educator, the pure leaven that leaveneth the world of being, and furnisheth the power through which the arts and wonders of the world are made manifest.

Bahá’u’lláh, Gleanings from the Writings of Bahá’u’lláh, p. 161

That which will leaven the human world is a love that will insure the abandonment of pride, oppression and hatred.

‘Abdu’l-Bahá, Divine Philosophy, p. 45

Even though outwardly the number of the friends has not been increasing so rapidly, yet the spirit has not remained idle. The leaven of spirituality has been working, and when the time will come it will manifest itself in a sudden awakening. All that we need is a little more courage, perseverance and patience. There are many important men that are attentively watching the progress of the Faith but are reluctant to come forward and extend a helping hand. In time they will, and then we shall see the Cause of God spread by leaps and bounds.

Shoghi Effendi, The Unfolding Destiny of the British Bahá’í Community, p. 430

From Alaska to Chile, the Americas are astir with the leavening influences of the rising Order of the newborn Revelation.

Shoghi Effendi, Messages to America, p. 55

In a world the structure of whose political and social institutions is impaired, whose vision is befogged, whose conscience is bewildered, whose religious systems have become anemic and lost their virtue, this healing Agency, this leavening Power, this cementing Force, intensely alive and all-pervasive, has been taking shape, is crystallizing into institutions, is mobilizing its forces, and is preparing for the spiritual conquest and the complete redemption of mankind. Though the society which incarnates its ideals be small, and its direct and tangible benefits as yet inconsiderable, yet the potentialities with which it has been endowed, and through which it is destined to regenerate the individual and rebuild a broken world, are incalculable.

Shoghi Effendi, The World Order of Bahá’u’lláh, p. 195

It is a great pleasure and privilege to me to enter into direct, and I trust, permanent correspondence with those faithful friends of ‘Abdu’l-Bahá, who though few in number and scattered over that vast and flourishing country, will I trust act as a powerful leaven to the mass of that spiritually-minded people. Though its people be firmly entrenched in their religious sectarianism and strongly attached to their religious doctrines and traditions, yet who can doubt that with courage and persistence, kindliness and wisdom, the all-conquering words of Bahá’u’lláh can fail to break down all these barriers of prejudice and religious exclusiveness and conquer this longstanding stronghold of sectarian belief!

Shoghi Effendi, Messages to Canada, p. 3

May this community, the leaven placed by the hands of Providence in the midst of a people belonging to a nation, likewise young, dynamic, richly endowed with material resources, and assured of a great material prosperity by ‘Abdu’l-Bahá, play its part not only in lending a notable impetus to the world-wide propagation of the Faith it has espoused, but contribute, as its resources multiply and as it gains in stature, to the spiritualization and material progress of the nation of which it forms so vital a part.

Shoghi Effendi, Messages to Canada, p. 23

Shoghi Effendi wishes me to assure you of his prayers and  26  expresses his hope to see the small groups in India and Burma develop into important centres radiating their activities to all the country around and becoming the leaven of goodness in that extensive land.

Shoghi Effendi, Messages to the Indian Subcontinent, p. 25

The American Bahá’í Community, the leaven destined to leaven the whole, cannot hope, at this critical juncture in the fortunes of a struggling, perilously situated, spiritually moribund nation, to either escape the trials with which this nation is confronted, nor claim to be wholly immune from the evils that stain its character. At so critical a period, at so challenging an hour, the members of a community, invested by ‘Abdu’l-Bahá with a primacy which can, through neglect and apathy, be allowed to lose its vital power and driving force, are immersed in a task, and are faced with responsibilities, which a World Spiritual Crusade,..has thrust upon them before the eyes of their admiring and expectant sister communities throughout the world.

Shoghi Effendi, Citadel of Faith, p. 127

The Bahá’ís are the leaven of God, which must leaven the lump of their nation. In direct ratio to their success will be the protection vouchsafed, not only to them but to their country. These are the immutable laws of God, from which there is no escape: "For unto whomsoever much is given, of him shall be much required."

Shoghi Effendi, Lights of Guidance, p. 136

The Community of the Most Great Name, the leaven that must leaven the lump, the chosen remnant that must survive the rolling up of the old, discredited, tottering order, and assist in the unfoldment of a new one in its stead, is standing ready, alert, clear-visioned, and resolute.

Shoghi Effendi, Lights of Guidance, p. 132

The companions of God are, in this day, the lump that must leaven the peoples of the world. They must show forth such trustworthiness, such truthfulness and perseverance, such deeds and character that all mankind may profit by their example.

Shoghi Effendi, Advent of Divine Justice, p. 23

The people of the world are teeming millions, the Bahá’ís only a handful, yet they are the precious leaven that must leaven the lump.

Shoghi Effendi, Lights of Guidance, p. 279

The significance of this dynamic spiritual leaven cast into the life of the world for the reorientation of the minds of men [Bahá’u’lláh’s Hidden Words], the edification of their souls and the rectification of their conduct can best be judged by the description of its character given in the opening passage by its Author: "This is that which hath descended from the Realm of Glory, uttered by the tongue of power and might, and revealed unto the Prophets of old. We have taken the inner essence thereof and clothed it in the garment of brevity, as a token of grace unto the righteous, that they may stand faithful unto the Covenant of God, may fulfill in their lives His trust, and in the realm of spirit obtain the gem of Divine virtue.

Shoghi Effendi, God Passes By, p. 139-40

In the degree to which Bahá’í communities embody the distinguishing characteristics of Bahá’í life and attract, by their unity, their steadfastness, their radiance and good reputation, the interest and eventual whole-hearted support of their fellow citizens. This is the magnet which will attract the masses to the Cause of God, and the leaven that will transform human society.

Universal House of Justice, NSA – USA, Developing Distinctive Bahá’í Communities

The prophets and the messengers have come in order to guide mankind to the straight path of the True One . . . They are the leaven of existence and the greatest means for the appearance of sciences and arts in this world.

Compilations, Bahá’í Scriptures, p. 404

The relationship of Shoghi Effendi to the pilgrims, his courtesy as a host, his kindness shown to them in so many little ways, the things he so openly discussed with them, had a tremendous effect on the work the Bahá’ís were accomplishing in so many countries, for when these fortunate believers returned to their own communities they acted as a leaven, stimulating their fellow Bahá’ís to greater efforts, making the Guardian a more real person to those who had not been privileged to meet him face to face, creating a sense of nearness both to him and to the World Centre that by any other method would have been hard to achieve.

Ruhiyyih Khanum, The Priceless Pearl, p. 132