Journal of Discourses 24:184 “Has there ever been a doctrine declared by the authorities of this Church, as a part of the Gospel of Jesus Christ, that they have had to take back or modify? Not one. Has there been anything in the organization that has had to be perfected? No. The organization was as perfect in theory—being revealed of God—50 years ago as it is today…That constitutes the strength of this work. It is its infallibility. Not that man connected with it is infallible, for he is fallible; but the work itself, its principles, and everything connected with it, is infallible, having a divine origin, being revealed of God.” — George Q. Cannon, Salt Lake City, July 15, 1883
Galatians 1:8 “But though we, or an angel from heaven, preach any other gospel unto you than that which we have preached unto you, let him be accursed.”
What Mr. Cannon didn’t say is how the Church was already under investigation by the Feds for their unlawful practice of polygamy. No less than Abraham Lincoln had placed sanctions on them for it. For more info, see article on the chain of events.
If their gospel was truly perfect why did polygamy stop?
Furthermore, if they were immutable, why did Joseph Smith claim to have continuing revelations?