When do you think the dispensation of Jesus Christ came to an end? 1817?
Technically speaking, it came to an end around 632 AD, since that is when the next Manifestation of God appeared and the Qur’an was revealed, but the new age was not ushered in until 1844, when the Bab appeared and prepared the way for Baha’u’llah, who appeared about nine years later.
How does the teaching of Baha'u'llah and others demonstrate 'a progressive revelation'? What has been added to the teaching and person of Jesus Christ since 1817?
What has been added was added after the Bible was canonized, and it is everything that has been revealed by Muhammad in the Qur’an and everything that was revealed in the Writings of Baha’u’llah.
The reason Baha’u’llah was sent by God is rather simple.
“The vitality of men’s belief in God is dying out in every land; nothing short of His wholesome medicine can ever restore it. The corrosion of ungodliness is eating into the vitals of human society; what else but the Elixir of His potent Revelation can cleanse and revive it? Is it within human power, O Hakím, to effect in the constituent elements of any of the minute and indivisible particles of matter so complete a transformation as to transmute it into purest gold? Perplexing and difficult as this may appear, the still greater task of converting satanic strength into heavenly power is one that We have been empowered to accomplish. The Force capable of such a transformation transcendeth the potency of the Elixir itself. The Word of God, alone, can claim the distinction of being endowed with the capacity required for so great and far-reaching a change.”
Gleanings From the Writings of Bahá’u’lláh, p. 200
“The world is in travail, and its agitation waxeth day by day. Its face is turned towards waywardness and unbelief. Such shall be its plight, that to disclose it now would not be meet and seemly. Its perversity will long continue. And when the appointed hour is come, there shall suddenly appear that which shall cause the limbs of mankind to quake. Then, and only then, will the Divine Standard be unfurled, and the Nightingale of Paradise warble its melody.” Gleanings From the Writings of Bahá’u’lláh, pp. 118-119
A new remedy was needed for the ailments of humanity in this new age. The remedy that was revealed in the Bible no longer meets the needs of present-day society. The spiritual teachings in the Bible are eternal so they will always address the spiritual needs of mankind, but we also have to live in a material world, so God sent Baha’u’llah with the remedy to cure the ills society now faces so that eventually the Kingdom of God can be built on earth.
“The All-Knowing Physician hath His finger on the pulse of mankind. He perceiveth the disease, and prescribeth, in His unerring wisdom, the remedy. Every age hath its own problem, and every soul its particular aspiration. The remedy the world needeth in its present-day afflictions can never be the same as that which a subsequent age may require. Be anxiously concerned with the needs of the age ye live in, and center your deliberations on its exigencies and requirements.
We can well perceive how the whole human race is encompassed with great, with incalculable afflictions. We see it languishing on its bed of sickness, sore-tried and disillusioned. They that are intoxicated by self-conceit have interposed themselves between it and the Divine and infallible Physician. Witness how they have entangled all men, themselves included, in the mesh of their devices. They can neither discover the cause of the disease, nor have they any knowledge of the remedy. They have conceived the straight to be crooked, and have imagined their friend an enemy.” Gleanings From the Writings of Bahá’u’lláh, p. 213
“No man, however acute his perception, can ever hope to reach the heights which the wisdom and understanding of the Divine Physician have attained. Little wonder, then, if the treatment prescribed by the physician in this day should not be found to be identical with that which he prescribed before. How could it be otherwise when the ills affecting the sufferer necessitate at every stage of his sickness a special remedy?” Gleanings From the Writings of Bahá’u’lláh, p. 80
The only way in which we can know the absolute truth of God is through the perfect prophecy and declaration of His will. And even this is not enough. To know God's perfect will, we must have His Spirit WITHIN us. This is why the Messiah was sent ONCE and for all time; to baptise us with the Spirit of truth. By sending more than one Messiah one is left asking what was wrong with the first Messiah. What is wrong with the Holy Spirit baptism? If truth is absolute, there only needs to be ONE MESSIAH.
You are right about the Holy Spirit, but the Holy Spirit needs to be renewed in every age because it wanes over time, and that is why the vitality of men’s belief in God is dying out in every land. That is why God sends a new Messenger which is an educator of humanity.
“While the
Baha’i Faith does not discount these inexact criteria of the senses, Abdu’l-Baha explained in a
talk he gave in Chicago that we human beings need a divine educator to quicken our minds and harmonize divergent thoughts:
The prophets of God are the first educator. They bestow universal education upon man and cause him to rise from lowest levels of savagery to the highest pinnacles of spiritual development. … His Holiness Jesus Christ was an educator of humanity. His teachings were altruistic; His bestowal universal. He taught mankind by the power of the Holy Spirit and not through human agency, for the human power is limited whereas the divine power is illimitable and infinite. The influence and accomplishment of Christ will attest to this. … The purpose of this is to show that the holy Manifestations of God, the divine prophets, are the first teachers of the human race. They are universal educators and the fundamental principles they have laid down are the causes and factors of the advancement of nations.
Guided and quickened by the teachings of these prophets and messengers, and inspired by the energies of the Holy Spirit, we gain true knowledge.
The materialist may deny its existence, but Abdu’l-Baha, in a
talk he gave in Paris, explained its power to inspire and educate humans:
An humble man without learning, but filled with the Holy Spirit, is more powerful than the most nobly-born profound scholar without that inspiration. He who is educated by the Divine Spirit can, in his time, lead others to receive the same Spirit.
The Baha’i teachings confirm that the foremost favor vouchsafed by the Almighty is this divine gift of knowledge and understanding.”
https://bahaiteachings.org/what-is-reality-can-senses-understand?