The prophet who was to prepare the way before the Messiah was also a doctrine taught in the plates of brass. Isaiah is the obvious source of Lehi’s teachings since he uses almost the verbatim language of the present text of Isaiah. However the text quoted by Lehi is much more complete, and it contains the words spoken by John the Baptist at the time of Jesus’ baptism (v. 8). This suggests that some plain and precious parts of the text of Isaiah have been lost.
After quoting what Lehi said, Nephi adds some of the other things Lehi taught, where John would baptize, and that he would bear record of having baptized the Lamb of God (vv. 9–10). Bethabara, the place where he would baptize, is confirmed in the Gospel of John: “These things were done in Bethabara beyond Jordan, where John was baptizing” (John 1:28). The other synoptic Gospels give only a general description, i.e., “all the country about Jordan” (Luke 3:3; see also Matthew 3:1 and Mark 1:4–5), which has led to much speculation among scholars. While the location of Bethabara is not known, it does give us a specific area to search out.
The Book of Mormon states that “after he had baptized the Messiah with water, he should behold and bear record that he had baptized the Lamb of God” (v. 10). The Gospel of John states: “The next day John seeth Jesus coming unto him, and saith, Behold the Lamb of God, which taketh away the sin of the world” (John 1:29). Thus the Book of Mormon bears record of the Gospel of John, and the Gospel of John bears record of the Book of Mormon. As Mormon later testified, “if ye believe [the Bible] ye will believe the [Book of Mormon] also” (Mormon 7:9).
The dwindling of the Jews in unbelief [the apostasy], the slaying of the Messiah, and his rising from the dead (v. 11) are historically accurate. The Book of Mormon is again a second witness to these events having been prophesied (see 1 Nephi 19:10, quoted later under 1 Nephi 11:26–29). The Messiah being manifest to the Gentiles by the Holy Ghost (v. 11) is not a personal appearance. As Jesus taught the Nephites when he appeared to them after his resurrection, “the Gentiles should not at any time hear my voice—that I should not manifest myself unto them save it were by the Holy Ghost” (3 Nephi 15:23).