Thanks, I never saw that quote.
I was not implying that everyone would become a Baha'i. There is no reason to believe there will be one common faith during the Dispensation of Baha'u'llah. There will probably be another Messenger(s) of God and another religion(s) before there is "one common faith."
On the other hand, once everyone knows about Baha'u'llah, as the passage below indicates will happen, it is possible that everyone will become a Baha'i, although there is no away to know when that will happen.
“Warn and acquaint the people, O Servant, with the things We have sent down unto Thee, and let the fear of no one dismay Thee, and be Thou not of them that waver. The day is approaching when God will have exalted His Cause and magnified His testimony in the eyes of all who are in the heavens and all who are on the earth.” Gleanings From the Writings of Bahá’u’lláh, p. 248
Apparently you didn't see the rest of my post:
This is the changeless Faith of God, eternal in the past, eternal in the future.
, “Gleanings from the Writings of Bahá’u’lláh” , 70.2
This implies to me to begin with that one faith means that eternal faith proclaimed by all Messengers, that is the spiritual essence of them.
In my opinion, I also don't think the world will have one religion in the next Dispensation. The union of all it's peoples is clearly destined for this Dispensation.
God’s purpose is none other than to usher in, in ways He alone can bring about, and the full significance of which He alone can fathom, the Great, the Golden Age of a long-divided, a long-afflicted humanity. Its present state, indeed even its immediate future, is dark, distressingly dark. Its distant future, however, is radiant, gloriously radiant — so radiant that no eye can visualize it.
Shoghi Effendi, “The Promised Day is Come” , 286
This will indeed be the fitting climax of that process of integration which, starting with the family, the smallest unit in the scale of human organization, must, after having called successively into being the tribe, the city-state, and the nation, continue to operate until it culminates in the unification of the whole world, the final object and the crowning glory of human evolution on this planet. It is this stage which humanity, willingly or unwillingly, is resistlessly approaching. It is for this stage that this vast, this fiery ordeal which humanity is experiencing is mysteriously paving the way. It is with this stage that the fortunes and the purpose of the Faith of Bahá’u’lláh are indissolubly linked. It is the creative energies which His Revelation has released in the “year sixty,” and later reinforced by the successive effusions of celestial power vouchsafed in the “year nine” and the “year eighty” to all mankind, that have instilled into humanity the capacity to attain this final stage in its organic and collective evolution. It is with the
Golden Age of His Dispensation that the consummation of this process will be forever associated. It is the structure of His New World Order, now stirring in the womb of the administrative institutions He Himself has created, that will serve both as a pattern and a nucleus of that world commonwealth which is the sure, the inevitable destiny of the peoples and nations of the earth.
Shoghi Effendi, “The Promised Day is Come” , 290
I will add here that I believe that it is unreasonable for everyone to believe in one religion at any time, given how different people have different opinions, and different spiritual susceptibilities. Is it reasonable that everyone in the world will be a true seeker? Some people will always cling to the former religion.