Is the Book of Mormon also scripture? What about the Koran?
A pointless question because it leaves open 5 things
1) Religions are not all wrong or all correct for the most part
2) The Faith comes before the expression in writing so the Church is superior to the revelation, you don't go to the bookstore,get a Bible, interpret willy-nilly and that makes you a Jew or Christian !!
3) The same thing can come from human speculation as from God by revelation but the difference is obviously enormous.
4) If you read conversion stories, many come up by partial truths to full truth. I recommend the stories of Messianic Jews to convince you of this.
5) God can use (your) error to teach you truth. As Augustine says: The desire to pray is itself a prayer.
Now let's turn it around
Newman says it is against any charitable belief in God to try to weed out as you do
"I do not undervalue at all the advantage of institutions which, though not Catholic, keep out evils worse than themselves. Some restraint is better than none: systems which do not simply inculcate divine truth, yet serve to keep men from being utterly hardened against it, when at length it addresses them; they preserve a certain number of revealed doctrines in the popular mind; they familiarize it to Christian ideas; they create religious associations; and thus, remotely and negatively, they may even be said to prepare and dispose the soul in a certain sense for those inspirations of grace, which, through the merits of Christ, are freely given to all men for their salvation, all over the earth. It is a plain duty, then, not to be forward in destroying religious institutions, even though not Catholic, if we cannot replace them with what is better;
but , from fear of injuring them, to shrink from saving the souls of the individuals who live under them, would be worldly wisdom, treachery to Christ, and uncharitableness to His redeemed. "
AND
Newman shows that there is true conversion and false converson , again obvious to anyone who's undergone conversion
"True religion is the summit and perfection of false religions; it combines in one whatever there is of good and true separately remaining in each . . . . So that, in matter of fact, if a religious mind were educated in and sincerely attached to some form of heathenism or heresy, and then were brought under the light of truth, it would be drawn off from error into the truth, not by losing what it had, but by gaining what it had not, not by being unclothed, but by being “clothed upon.”
True conversion is ever of a positive, not a negative character "
