It is a loaded question for certain.
What I had in mind was how the Manifestations of God are essentially one and the same.
The Bearers of the Trust of God are made manifest unto the peoples of the earth as the Exponents of a new Cause and the Revealers of a new Message. Inasmuch as these Birds of the celestial Throne are all sent down from the heaven of the Will of God, and as they all arise to proclaim His irresistible Faith, they, therefore, are regarded as one soul and the same person. For they all drink from the one Cup of the love of God, and all partake of the fruit of the same Tree of Oneness.
“In thine esteemed letter thou hadst inquired which of the Prophets of God should be regarded as superior to others. Know thou assuredly that the essence of all the Prophets of God is one and the same. Their unity is absolute. God, the Creator, saith: There is no distinction whatsoever among the Bearers of My Message. They all have but one purpose; their secret is the same secret. To prefer one in honor to another, to exalt certain ones above the rest, is in no wise to be permitted. Every true Prophet hath regarded His Message as fundamentally the same as the Revelation of every other Prophet gone before Him.”
A selection of passages from the Writings of Bahá’u’lláh, compiled and translated by Shoghi Effendi, including extracts from Epistle to the Son of the Wolf, the Kitáb-i-Íqán, and the Kitáb-i-Aqdas, as well as other Tablets.
www.bahai.org
However, there is also this passage:
“These Manifestations of God have each a twofold station.
One is the station of pure abstraction and essential unity. In this respect, if thou callest them all by one name, and dost ascribe to them the same attributes, thou hast not erred from the truth. Even as He hath revealed: “No distinction do We make between any of His Messengers.” For they, one and all, summon the people of the earth to acknowledge the unity of God, and herald unto them the Kaw
thar of an infinite grace and bounty. They are all invested with the robe of prophethood, and are honored with the mantle of glory.....
The other station is the station of distinction, and pertaineth to the world of creation, and to the limitations thereof. In this respect, each Manifestation of God hath
a distinct individuality, a definitely prescribed mission, a predestined revelation, and specially designated limitations. Each one of them is known by a different name, is characterized by a special attribute, fulfils a definite mission, and is entrusted with a particular Revelation.”
Gleanings From the Writings of Bahá’u’lláh, pp. 50-52
The first part of the Religion of God which refers to
spiritual truth is the same in every religion, so as your passage above says "Every true Prophet hath regarded His Message as fundamentally the same as the Revelation of every other Prophet gone before Him.” However, the second part of the Religion of God which refers to
material things is different in each religion. It changes in every age with each new Manifestation of God to accommodate the needs of the times.
There is also a distinction between the primary message that the Manifestations of God bring. Religion is associated with social evolution. Thus the primary mission of each Messenger of God changes from age to age as humanity evolves. The mission and associated message is
progressive, each mission building upon the previous one
“The Revelation associated with the Faith of Jesus Christ focused attention primarily on the redemption of the individual and the molding of his conduct, and stressed, as its central theme, the necessity of inculcating a high standard of morality and discipline into man, as the fundamental unit in human society. Nowhere in the Gospels do we find any reference to the unity of nations or the unification of mankind as a whole. When Jesus spoke to those around Him, He addressed them primarily as individuals rather than as component parts of one universal, indivisible entity.......
The Faith of Islám, the succeeding link in the chain of Divine Revelation, introduced, as Bahá’u’lláh Himself testifies, the conception of the nation as a unit and a vital stage in the organization of human society, and embodied it in its teaching. This indeed is what is meant by this brief yet highly significant and illuminating pronouncement of Bahá’u’lláh: “Of old [Islamic Dispensation] it hath been revealed: ‘Love of one’s country is an element of the Faith of God.’” This principle was established and stressed by the Apostle of God, inasmuch as the evolution of human society required it at that time. Nor could any stage above and beyond it have been envisaged, as world conditions preliminary to the establishment of a superior form of organization were as yet unobtainable.
The conception of nationality, the attainment to the state of nationhood, may, therefore, be said to be the distinguishing characteristics of the MuHammadan Dispensation, in the course of which the nations and races of the world, and particularly in Europe and America, were unified and achieved political independence.....
“One of the great events,” ‘Abdu’l-Bahá has, in His “Some Answered Questions,” affirmed, “which is to occur in the Day of the manifestation of that Incomparable Branch [Bahá’u’lláh] is the hoisting of the Standard of God among all nations. By this is meant that all nations and kindreds will be gathered together under the shadow of this Divine Banner, which is no other than the Lordly Branch itself, and will become a single nation. Religious and sectarian antagonism, the hostility of races and peoples, and differences among nations, will be eliminated.
All men will adhere to one religion, will have one common faith, will be blended into one race, and become a single people. All will dwell in one common fatherland, which is the planet itself.”
The Promised Day Is Come, pp. 119-121
I believe if one sincerely follows to the best of their ability any of the Manifestations of God there is also no distinction. The Prophets of God are One and the 'Word of God' is the 'Word of God' regardless of the Manifestation.
If there is no distinction, why would it matter if people embrace the Baha'i Faith? Why not just continue to have a bunch of separate religions forever?
If you believe what Baha'u'llah wrote, clearly that is not what God has ordained.
“That which the Lord hath ordained as the sovereign remedy and mightiest instrument for the healing of all the world is the union of all its peoples in one universal Cause, one common Faith. This can in no wise be achieved except through the power of a skilled, an all-powerful and inspired Physician. This, verily, is the truth, and all else naught but error.”
The Summons of the Lord of Hosts, p. 91
Why teach the Faith if people are not going to embrace it and instead just say "oh, that's interesting?"
It sure seemed to matter to Baha'u'llah that people embrace His Cause, which is the Cause of God.
In the following passages 'the Cause of God' and 'His Cause' are the Cause of Baha'u'llah, i.e. the Baha'i Faith.
“Say: Teach ye the Cause of God, O people of Bahá, for God hath prescribed unto every one the duty of proclaiming His Message, and regardeth it as the most meritorious of all deeds.”
Gleanings, p. 278
“Unloose your tongues, and proclaim unceasingly His Cause. This shall be better for you than all the treasures of the past and of the future, if ye be of them that comprehend this truth.”
Gleanings, p. 330
Referring to Baha’u’llah as “Him Whom God shall make manifest” the Bab wrote:
“Wert thou to open the heart of a single soul by helping him to embrace the Cause of Him Whom God shall make manifest, thine inmost being would be filled with the inspirations of that august Name… For indeed if thou dost open the heart of a person for His sake, better will it be for thee than every virtuous deed; since deeds are secondary to faith in Him and certitude in His Reality. XVII, 15.”
Selections From the Writings of the Báb, p. 133