Compare the two passages
LDS Discussions argues that Mormon 9:22–24 reproduces language from Mark 16:15–18, part of a longer ending that was likely added to Mark. The overlap goes beyond a familiar biblical style. Both passages give a commission to preach, connect belief and baptism with salvation, and list the same five signs in the same order. These include speaking in new tongues, handling serpents, surviving a deadly drink, and healing the sick. Mormon 9:24 is nearly word for word with Mark 16:17–18. The wording already appears in the Book of Mormon’s first edition. LDS Discussions · Mark 16:15–18 · Mormon 9:22–25 · 1830 Book of Mormon, p. 537
What the early witnesses show
Two fourth-century Greek manuscripts, Codex Sinaiticus and Codex Vaticanus, end Mark at 16:8. Sinaiticus starts Luke on the same page. Vaticanus leaves a blank column before Luke begins on the next page. Other manuscripts include verses 9–20, sometimes alongside a different ending. The NET editors weigh those variants together with differences in vocabulary and the abrupt transition to verse 9. They judge the longer ending likely secondary. The possibility that Mark once had a different ending is a separate question. Codex Sinaiticus, folio 228r · Codex Vaticanus, p. 1303 · NET textual note on Mark 16:9
Irenaeus quotes what is now Mark 16:19 and attributes it to Mark around AD 180, well before those two surviving manuscripts were copied. That establishes early circulation of at least part of the ending. An early quotation cannot tell us whether Mark wrote it or whether each saying in the longer ending came from Jesus. Irenaeus, Against Heresies 3.10.5
What would explain the English match?
The simplest critical argument is that a modern writer took the commission and signs from the King James Bible and put them into Moroni’s account. The length and order of the matching language give that argument weight. The Book of Mormon’s own account gives another way to understand the passage. Moroni presents the words as Jesus’s instruction to disciples, including those who would remain on earth. That setting fits the book’s account of the risen Christ commissioning Nephite disciples. Scripture Central proposes that familiar King James wording could have supplied the English expression of a related commission. Mormon 9:22–25 · 3 Nephi 28:4–9 · Scripture Central’s response
A secondary ending can preserve an earlier tradition. Acts describes Paul surviving a viper bite, and Eusebius reports that Papias told a story of Justus Barsabbas drinking poison without harm. Those stories show that individual motifs circulated outside this passage. They give us neither an independent record of Jesus giving the full list nor a basis for deciding which account influenced another. Acts 28:3–9 · Eusebius, Church History 3.39.9
Accepting that Mark 16:9–20 is probably secondary leaves the Latter-day Saint explanation available. The harder question is whether an English translation of an earlier commission would use this much of the KJV passage in the same order. The Church’s translation essay describes Joseph dictating the English text and leaves the source of this particular phrasing open. Compare what each explanation needs to account for in the words on the page. Book of Mormon Translation