There are many non mormons here who know EXACTLY what the LDS believe. We’ve been there, done that (read the book, saw the movie, wore the garments).
To the LDS prophets ARE infallible. The ONLY time *I* have ever heard the “they are not infallible” argument is when past teachings conflict with current view. The LDS song “Follow the Prophet” has a line “he will not lead you astray”.
the Ward Teachers’ message for June 1945 instructed members that “when the prophet speaks the thinking has been done.”
President Brigham Young has assured us we can have complete confidence in the prophets. He said: “The Lord Almighty leads this Church, and he will never suffer you to be led astray. . .” (in Journal of Discourses, 9:289)
Regarding the “worship” of Joseph Smith. There is the LDS Hymn “praise to the man” (btw, only GOD deserves our praise). And here are numerous quotes about needing JS’s acceptance to get into the Celestial Kingdom (the only real ‘Heaven’):
If Joseph was verily a prophet . . . then his knowledge is of the most vital importance to the entire world. No man can reject that testimony without incurring the most dreadful consequences, for he cannot enter the kingdom of God (Doctrines of Salvation, vol. 1, Joseph Fielding Smith Jr., p. 189).
Heber C. Kimball, a member of the first Presidency under Brigham Young, said that the time would come when people would prize brother Joseph Smith as the Prophet of the Living God, and look upon him as a God, and also upon Brigham Young, our Governor in the Territory of Deseret (Journal of Discourses, vol. 5, p. 88).
These are from another prophet Brigham Young:
. I am an Apostle of Joseph Smith. . . . all who reject my testimony will go to hell, so sure as there is one, no matter whether it be hot or cold . . . (Journal of Discourses, vol. 3, p. 212)
. . . no man or woman in this dispensation will ever enter into the celestial kingdom of God without the consent of Joseph Smith. . . . Every man and woman must have the certificate of Joseph Smith, junior, as a passport to their entrance into the mansion where God and Christ are . . . I cannot go there without his consent. . . . He reigns there as supreme a being in his sphere, capacity, and calling, as God does in heaven (Journal of Discourses, vol. 7, p. 289).
I will now give my scripture”Whosoever confesseth that Joseph Smith was sent of God . . . that spirit is of God; and every spirit that does not confess that God has sent Joseph Smith, and revealed the everlasting Gospel to and through him, is of Anti-christ . . . (Journal of Discourses, vol. 8, p. 176 ).
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