I have two questions about the 13th article of faith. First, where in the scriptures do we find “the admonition of Paul”? Second, where it says “We believe all things, we hope all things,” What are these “things?” There are “things” I don’t believe or hope for. Are the “things” meant to mean eternal truths, the scriptures, the gospel or something else?
It appears that Joseph Smith drew on Philippians 4:8 in drafting the thirteenth Article of Faith. It reads:
“Finally, brethren, whatsoever things are true, whatsoever things are honest, whatsoever things are just, whatsoever things are pure, whatsoever things are lovely, whatsoever things are of good report; if there be any virtue, and if there be any praise, think on these things.”
I am inclined to agree with you that the idea of “believ[ing]”, “hop[ing]”, and “endur[ing]” all things does not mean we should be gullible; rather, it is that we should accept and endure true teachings while discerning between that which is of God and that which is not. It may be noteworthy to point out that in 2 Timothy 4:3, Paul warns Timothy about those who “will not endure sound doctrine; but after their own lusts shall they heap to themselves teachers, having itching ears”.
There is a good article that came out in the Church News in 1992. You can read it here.