“Nature is God's Will and is its expression in and through the contingent world.”

Say: Nature in its essence is the embodiment of My Name, the Maker, the Creator. Its manifestations are diversified by varying causes, and in this diversity there are signs for men of discernment. Nature is God's Will and is its expression in and through the contingent world. It is a dispensation of Providence ordained by the Ordainer, the All-Wise. Were anyone to affirm that it is the Will of God as manifested in the world of being, no one should question this assertion. It is endowed with a power whose reality men of learning fail to grasp. Indeed a man of insight can perceive naught therein save the effulgent splendour of Our Name, the Creator. Say: This is an existence which knoweth no decay, and Nature itself is lost in bewilderment before its revelations, its compelling evidences and its effulgent glory which have encompassed the universe. 

- Baha'u'llah  ('Tablets of Baha'u'llah revealed after the Kitab-i-Aqdas')

“The religion of God and His divine law”

The religion of God and His divine law are the most potent instruments and the surest of all means for the dawning of the light of unity amongst men. The progress of the world, the development of nations, the tranquillity of peoples, and the peace of all who dwell on earth are among the principles and ordinances of God. Religion bestoweth upon man the most precious of all gifts, offereth the cup of prosperity, imparteth eternal life, and showereth imperishable benefits upon mankind. 

- Bahá'u'lláh  ('Tablets of Bahá'u'lláh revealed after the Kitáb-i-Aqdas'; The Compilation of Compilations, vol. III, Social and Economic Development)

“open his mind and heart to the blessing of the spirit”

When man allows the spirit, through his soul, to enlighten his understanding, then does he contain all Creation... But on the other hand, when man does not open his mind and heart to the blessing of the spirit, but turns his soul towards the material side, towards the bodily part of his nature, then is he fallen from his high place and he becomes inferior to the inhabitants of the lower animal kingdom.... 

- ‘Abdu’l-Baha  (‘Paris Talks: Addresses given by 'Abdu'l-Bahá in Paris in 1911-1912’, The Compilation of Compilations, Vol. II, The Importance of Prayer, Meditation and the Devotional Attitude)

“there always have been Manifestations of God”

Regarding your questions: the only reason there is not more mention of the Asiatic Prophets is because Their names seem to be lost in the mists of ancient history. Buddha is mentioned, and Zoroaster, in our Scriptures -- both non-Jewish Prophets or non-Semitic Prophets. We are taught there always have been Manifestations of God, but we do not have any record of Their names. 

- Shoghi Effendi  (From a letter dated 4 October 1950 written on behalf of Shoghi Effendi to an individual believer; The Compilation of Compilations, vol. I, Extracts from the Baha’i Writings on Buddha, Krishna, Zoroaster, and related subjects)

The reason the Prophets “have appeared in this world”

The Prophets have appeared in this world with the mission that human souls may become the expressions of the Merciful, that they may be educated and developed, attain to love and amity and establish peace and agreement. 

- ‘Abdu’l-Baha  (Excerpt from a talk given on 21 April 1912 in Washington D.C.; ‘The Promulgation of Universal Peace: Talks Delivered by ‘Abdu’l-Bahá during His Visit to the United States and Canada in 1912’)

“a seeing heart”

O thou possessor of a seeing heart! Although, materially speaking, thou art deprived of physical sight, yet, praise be to God, spiritual insight is thine. Thy heart seeth and thy spirit heareth. Bodily sight is subject to a thousand maladies and assuredly will ultimately be lost. Thus no importance should be attached to it. But the sight of the heart is illumined. It discerneth and discovereth the divine Kingdom. It is everlasting and eternal. Praise God, therefore, that the sight of thy heart is illumined, and the hearing of thy mind responsive.

Each of the meetings ye have organized, wherein ye feel heavenly emotions and comprehend realities and significances, is like unto the firmament, and those souls are as resplendent stars shining with the light of guidance.

Happy is the soul that seeketh, in this brilliant era, heavenly teachings, and blessed is the heart which is stirred and attracted by the love of God. 

- ‘Abdu’l-Baha  (‘Selections from the Writings of ‘Abdu’l-Baha’)

“the Most Mighty Branch”

The Will of the divine Testator is this: It is incumbent upon the Aghsan, the Afnan and My Kindred to turn, one and all, their faces towards the Most Mighty Branch. Consider that which We have revealed in Our Most Holy Book: 'When the ocean of My presence hath ebbed and the Book of My Revelation is ended, turn your faces toward Him Whom God hath purposed, Who hath branched from this Ancient Root.' The object of this sacred verse is none other except the Most Mighty Branch [Abdu'l-Bahá]. Thus have We graciously revealed unto you Our potent Will, and I am verily the Gracious, the All-Powerful. Verily God hath ordained the station of the Greater Branch [Muhammad Ali] to be beneath that of the Most Great Branch [Abdu'l-Bahá]. He is in truth the Ordainer, the All-Wise. We have chosen 'the Greater' after 'the Most Great', as decreed by Him Who is the All-Knowing, the All-Informed. 

- Baha'u'llah  ('Tablets of Baha'u'llah revealed after the Kitab-i-Aqdas')

“Verily, We behold you from Our realm of glory…”

Let not your hearts be perturbed, O people, when the glory of My Presence is withdrawn, and the ocean of My utterance is stilled. In My presence amongst you there is a wisdom, and in My absence there is yet another, inscrutable to all but God, the Incomparable, the All-Knowing. Verily, We behold you from Our realm of glory, and shall aid whosoever will arise for the triumph of Our Cause with the hosts of the Concourse on high and a company of Our favoured angels.

- Baha'u'llah  ('The Kitab-i-Aqdas')

The Báb’s “sacred remains constitute the heart and center of what may be regarded as nine concentric circles”

For, just as in the realm of the spirit, the reality of the Báb has been hailed by the Author of the Bahá'í Revelation as "The Point round Whom the realities of the Prophets and Messengers revolve," so, on this visible plane, His sacred remains constitute the heart and center of what may be regarded as nine concentric circles, paralleling thereby, and adding further emphasis to the central position accorded by the Founder of our Faith to One "from Whom God hath caused to proceed the knowledge of all that was and shall be," "the Primal Point from which have been generated all created things." 

- Shoghi Effendi  (‘Citadel of Faith’)

To be “enkindled” and “humble and lowly” when teaching the Faith

The teacher, when teaching, must be himself fully enkindled, so that his utterance, like unto a flame of fire, may exert influence and consume the veil of self and passion. He must also be utterly humble and lowly so that others may be edified, and be totally self-effaced and evanescent so that he may teach with the melody of the Concourse on high -- otherwise his teaching will have no effect. 

- 'Abdu'l-Baha  ('Selections from the Writings of ‘Abdu'l-Baha')

“Communication is not confined to writing”

O thou son of the associate and companion of ‘Abdu’l-Baha! You brought many letters with you from those regions, but on account of the great disturbance it was not possible to write the answers. You saw what a commotion was set up in the Blessed Spot [1] through the instigation of the jealous brother. It still continues. Therefore you must apologize: Say that ‘Abdu’l-Baha has considered every one of the letters with the eyes of the spirit, has read each, and through the valid messenger—that is, through the spiritual susceptibilities—has sent each the message of peace and greeting. Therefore, let them turn to the blessed and Radiant Spot with a pure heart and an attracted spirit, that they may receive answer through the lights radiating therefrom.

Communication is not confined to writing. This is a trace, while the spiritual message is fruitful and effective.  That is the essential, and without it communication is useless. 

- ‘Abdu’l-Baha  (‘Tablets of ‘Abdu’l-Baha’, vol. 1)

[1] Akka

To “regard His [the Báb’s] dispensation together with that of Bahá'u'lláh as forming one entity, the former being an introductory to the advent of the latter”

Though the teachings of the Bayan have been abrogated and superseded by the laws of Aqdas, yet due to the fact that the Bab considered Himself as the forerunner of Bahá'u'lláh we should regard His dispensation together with that of Bahá'u'lláh as forming one entity, the former being an introductory to the advent of the latter. Just as the advent of John the Baptist -- who according to various authorities was Himself the originator of laws which abrogated the teachings current among the Jews -- forms part of the Christian revelation, the advent of the Bab likewise forms an integral part of the Bahá'í Faith. 

- Shoghi Effendi  (From a letter dated 30 November 1930, written on behalf of Shoghi Effendi; printed in ‘The Unfolding Destiny of the British Baha'i Community’)

“the nearer you are to Cod, the further you are from the world”

Pray that your hearts may be cut from yourselves and from the world, that you may be confirmed by the Holy Spirit and filled with the fire of the love of Cod. The nearer you are to light, the further you are from the darkness; the nearer you are to heaven, the further you are from the earth; the nearer you are to Cod, the further you are from the world. 

- 'Abdu'l-Baha  (Words of ‘Abdu’l-Baha quoted by May Maxwell in ‘An Early Pilgrimage’, 1898)

The Báb & Bahá’u’lláh

And when Thou didst purpose to make Thyself known unto men, Thou didst successively reveal the Manifestations of Thy Cause, and ordained each to be a sign of Thy Revelation among Thy people, and the Day-Spring of Thine invisible Self amidst Thy creatures, until the time when, as decreed by Thee, all Thy previous Revelations culminated in Him Whom Thou hast appointed as the Lord of all who are in the heaven of revelation and the kingdom of creation, Him Whom Thou hast established as the Sovereign Lord of all who are in the heavens and all who are on the earth. He it was Whom Thou hast determined to be the Herald of Thy Most Great Revelation and the Announcer of Thy Most Ancient Splendor. In this Thou hadst no other purpose except to try them who have manifested Thy most excellent titles unto all who are in heaven and on earth. He it was Whom Thou hast commanded to establish His covenant with all created things.

And when Thy promise came to pass and the set time was fulfilled, He Who is the Possessor of all Names and Attributes was made manifest unto men. Thereupon all that were in the heavens and all that were on the earth were terror-stricken save those whom Thou didst keep under Thy protection and preserve within the shelter of Thy power and gracious providence. There befell Him, at the hands of such of Thy creatures as have transgressed against Thee, that which the tongue of no one of Thy servants can recount. 

- Baha'u'llah  ('Prayers and Meditations by Baha'u'llah')

“the fear of God impelleth man to hold fast to that which is good, and shun all evil”

When the Day-Star of Wisdom rose above the horizon of God's Holy Dispensation it voiced this all-glorious utterance: They that are possessed of wealth and invested with authority and power must show the profoundest regard for religion. In truth, religion is a radiant light and an impregnable stronghold for the protection and welfare of the peoples of the world, for the fear of God impelleth man to hold fast to that which is good, and shun all evil. Should the lamp of religion be obscured, chaos and confusion will ensue, and the lights of fairness and justice, of tranquillity and peace cease to shine. Unto this will bear witness every man of true understanding. 

- Baha'u'llah  ('Tablets of Baha'u'llah revealed after the Kitab-i-Aqdas’)

Book: "Abdu'l-Bahá in London"

Regarding "'Abdu'l-Bahá in London". Nothing can be considered scripture for which we do not have an original text. A verbatim record in Persian of His talks would of course be more reliable than one in English because He was not always accurately interpreted. However such a book is of value, and certainly has its place in our literature. 

- Shoghi Effendi  (From a letter written on behalf of Shoghi Effendi to an individual believer, dated 24 October 1947; ‘The Unfolding Destiny’)