There is no discussion to be had with a person who cannot accept Christianity due to their own bias against "sinful men", and instead want to have a conversation not from a common base (which is what the councils and the Creed represent: the dividing line between those who are within Christianity and those who are not), but from what of our scriptures that they will accept (after mutilating them, as you have done with John 17:21; the fathers, rather, understood this verse to be a reference to the homoousian reality of the Holy Trinity, e.g., St. Augustine writes in his
Tracte CX on John: "The Father, therefore, is in the Son, and the Son in the Father, in such a way as to be one, because they are of one substance"). This is not different than any non-Christian religion, as is obvious when looking at the parallels between Mormonism and the religions of others who claimed to be restoring the true faith that had been manipulated and filled with paganism by others.
Be that as it may, just for everyone's edification, the standard 27-book NT that is accepted by all Christian churches (some have more, but all have at least those 27) was first enumerated in the 39th festal (Easter) letter of our father HH St. Athanasius the Apostolic, the 20th Pope of the Coptic Orthodox Church of Alexandria, in 367 AD. It was subsequently accepted by other churches outside of Egypt, being confirmed (e.g.) at a synod in Carthage in 382.
It is also one tradition (in the Coptic Orthodox Church) that our father HH St. Athanasius authored the Nicene Creed, though other traditions say that he wrote it together with HG Bishop Hosius of Cordoba, and still others that it was collaborative effort between many of the assembled bishops. Point being, we have here a man who is ultimately responsible for promulgating the Biblical canon used by all Christian churches, who at least had a role in authoring the Creed which is used by the majority of churches as well as their symbol of belief, and so on...and the Mormons would have you believe that, as church leaders are sinful men, they can't possibly be correct regarding how to interpret that very same Bible that they themselves canonized and that very same faith that they laid down for us just as we continue to affirm today.
And while all the saints from the first century (including those taught by the apostles and the disciples themselves, such as St. Ignatius of Antioch, Anianus of Alexandria, etc.) onward got it wildly wrong, a farm boy in New York in the 19th century (I mistyped earlier; Mormonism is even younger than I remembered) somehow restored everything to how it was meant to be from the apostolic times until today...novel doctrines and books, "Reformed Egyptian", magical seeing stones and all.
You guys do remember how all that is in the Bible, right? The coming of Joseph Smith and his restoring of Christianity?
Yeah. Sure. But it is the rest of Christianity that has embraced "non-Biblical ideas", right?
