He taught Latter-day Saints that their religion gives them the right and privilege to accept all truth, and to reject false teachings and traditions.
“Mormonism is truth; and every man who embraces it feels himself at liberty to embrace every truth: consequently the shackles of superstition, bigotry, ignorance, and priestcraft, fall at once from his neck; and his eyes are opened to see the truth, and truth greatly prevails…”
“[T]he doctrine of the Latter-day Saints, is truth. … The first and fundamental principle of our holy religion is, that we believe that we have a right to embrace all, and every item of truth, without limitation or without being circumscribed or prohibited by the creeds or superstitious notions of men…”
“[T]he most prominent difference in sentiment between the Latter-day Saints and [the churches of his day] was, that the latter were all circumscribed by some peculiar creed, which deprived its members the privilege of believing anything not contained therein, whereas the Latter-day Saints … are ready to believe all true principles that exist, as they are made manifest from time to time.”
“I cannot believe in any of the creeds of the different denominations, because they all have some things in them I cannot subscribe to, though all of them have some truth. I want to come up into the presence of God, and learn all things; but the creeds set up [limits], and say, ‘Hitherto shalt thou come, and no further’ [Job 38:11]; which I cannot subscribe to.”
These quotations, and much more interesting material on the subject, appear in Chapter 22 of “Teachings of the Presidents of the Church: Joseph Smith”, which is studied by LDS men in their Sunday Priesthood meetings throughout 2008.