Doctrines were created by men, not by God or a Manifestation of God. Because men did not understand the scriptures they got together and decided upon Doctrines. Doctrines such as the Trinity, Jesus is God incarnate, the bodily resurrection, ascension and return of the same Jesus on a cloud, and that the indwelt Holy Spirit cannot be reconciled to the Baha’i Faith. Baha’u’llah and Abdu’l-Baha delineated the discrepancies so I find it best to just present the Writings rather than word it myself.
I see no reason to try to make the older religions “fit” the Baha’i Faith. They will never fit because they are different. What we all share in common are the spiritual verities which are eternal but what Baha’u’llah brought that was new cannot be reconciled to older belief systems. Their messages were for another time in history. They are not the remedy we need for today’s world and into the future. I just do not see the point of trying to make them fit the new age. Nowhere in the Writings does it say this is what we are to be doing.
“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.” Gleanings From the Writings of Bahá’u’lláh, p. 213
Baha’u’llah came and planted new plants. Had humanity not needed new plants God would not have sent a new Manifestation of God. If it had been possible, God would have waited for humans to tend the garden and remove the weeds and feed the remaining plants.
“In the beginning the tree was in all its beauty, and full of blossoms and fruits, but at last it became old and entirely fruitless, and it withered and decayed. This is why the True Gardener plants again an incomparable young tree of the same kind and species, which grows and develops day by day, and spreads a wide shadow in the divine garden, and yields admirable fruit. So it is with religions; through the passing of time they change from their original foundation, the truth of the Religion of God entirely departs, and the spirit of it does not stay; heresies appear, and it becomes a body without a soul. That is why it is renewed.” Some Answered Questions, p. 166
It is too late to restore the older religions to their original form; they cannot be restored and there is no need to restore them now that we have a new religion. Nowhere have the Baha’is been instructed to try to restore the older religions. We have only been instructed to work in unity and harmony with the adherents of the older religions.
“Through each and every one of the verses which the Pen of the Most High hath revealed, the doors of love and unity have been unlocked and flung open to the face of men. We have erewhile declared—and Our Word is the truth—: “Consort with the followers of all religions in a spirit of friendliness and fellowship.” Whatsoever hath led the children of men to shun one another, and hath caused dissensions and divisions amongst them, hath, through the revelation of these words, been nullified and abolished. From the heaven of God’s Will, and for the purpose of ennobling the world of being and of elevating the minds and souls of men, hath been sent down that which is the most effective instrument for the education of the whole human race.”
Gleanings From the Writings of Bahá’u’lláh, p. 95
Every new Manifestation of God renews the eternal spiritual verities but He starts over with a new plan for humanity. The Revelation of Baha’u’llah is
a new revelation from God. It is separate from the previous revelations, the most current in a successive chain of revelations which will continue into the future. Baha’u’llah had a new mission and a new message. The former revelations have been abrogated so I see no reason to try to make them “fit” with the Revelation of Baha’u’llah. They will never fit because the Baha’i Faith is not only an entirely new religion; it ushered in an entirely new religious cycle.
"In conclusion of this theme, I feel, it should be stated that the Revelation identified with Bahá’u’lláh abrogates unconditionally all the Dispensations gone before it, upholds uncompromisingly the eternal verities they enshrine, recognizes firmly and absolutely the Divine origin of their Authors, preserves inviolate the sanctity of their authentic Scriptures,”
Shoghi Effendi, God Passes By, p. 100