Mosiah 3:10

In Ephesians 3, Paul describes the “mystery of Christ” as something hidden from all previous generations but revealed in the apostolic era. In Ephesians 3:4–6, this mystery is that Gentiles are now equal heirs, members, and partakers in God’s promises through Christ—without the former distinctions of Jewish law. Paul reinforces in Colossians 1:26 and Romans 16:25 that this truth was not known in earlier ages, meaning it was not fully understood by Old Testament figures.

This is supported in Acts 10, where Peter struggles to accept Gentile inclusion even after revelation, and in Acts 15, where early Christians debate whether Gentiles must follow Jewish law. Likewise, Hebrews 11 and First Peter indicate that earlier prophets only saw partial foreshadowings of Christ, not the full picture.

In contrast, the Book of Mormon (e.g., 1 Nephi 10; 1 Nephi 14) portrays ancient prophets as clearly teaching about the Messiah, the gospel, and Gentile inclusion with New Testament-level clarity, including ideas similar to Romans 11.

This creates a chronological and theological conflict: if Paul is correct that this mystery was only revealed in the first century, then the Book of Mormon’s depiction of earlier prophets possessing that same knowledge suggests an anachronism—projecting later doctrine into an earlier time.

"When one begins to read the Book of Mormon, if he is well-acquainted with the Bible, he will at once be impressed with the large scale use of the biblical materials in the book. Not only is there an unskilled mimicking of the style of the King James Version, but there is an artificial clarity added to that portion of the Book of Mormon that claims to date from the Old Testament period. This contrived clarity is the result of writing back into that Old Testament period New Testament words, phrases and quotations, as well as the introduction of New Testament concepts and teachings into that time-frame... The usual Mormon defense is that such knowledge was supernaturally made known to the people in America, just as God in a vision showed Ezekiel that Jerusalem was about to fall and the temple to be destroyed, or Peter given a vision of Cornelius before he met him in person. Such an explanation might be more readily accepted if the Book of Mormon had presented its material in the format of a vision. Instead it introduces its material in much the same way that a nineteenth century frontier preacher introduced biblical quotations into his sermons. The frequency with which the Book of Mormon introduces this chronologically misplaced material into its text would require that God supernaturally provided this American colony with virtually the entire New Testament text, as well as those portions of the Old Testament which postdated their departure for America.... passages from the New Testament... are sprinkled generously into the speeches and sermons of the Book of Mormon characters in the same manner as one might find them in the sermons of a Methodist or Baptist preacher of Joseph Smith's day. This type of usage implies an acquaintance with the New Testament books themselves. Only after knowing the entire work can one select from it appropriate words and phrases to employ in this sermonic manner. It is naive to suggest that in every one of those instances God made known each of those biblical phrases and quotations so that the Old Testament Book of Mormon speakers could work them into their message. It is far more reasonable to believe that the insertions of such phrases and quotes came from one who already had the New Testament in hand before him while composing the Book of Mormon... The really fatal blow to the proposal that the New Testament material in the Old Testament portion of the Book of Mormon is due to Joseph Smith's employment of such phrases in the process of translating the book is that such material goes much deeper than the mere use of words and phrases. New Testament concepts, interpretations and theology are all worked into the text itself." -Wesley P. Walters, "The Use of the Old Testament in the Book of Mormon," (Master's thesis, Covenant Theological Seminary, St. Louis, Missouri, 1981), pp. 7, 10-13.

LDS author Grant Hardy writes, "In 1831, Alexander Campbell, one of the book's first critics (and certainly the first one to read it carefully), famously observed that it seemed to weigh in on all the popular religious questions of the day, including 'infant baptism, ordination, the trinity, regeneration, repentance, justification, the fall of man, the atonement, transubstantiation, fasting, penance, church government, religious experience, the call to the ministry , the general resurrection, eternal punishment, who may baptize, and even the question of freemasonry, republican government, and the right of the man.' This is a fair list, and references to these topics-or their analogous counterparts-can be found throughout the Book of Mormon." -Hardy, Understanding the Book of Mormon, p. 184