In the previous verse, verse 17, Nephi declared that Jehovah would do a marvelous work and a wonder. Here he defines that the marvelous work and a wonder would be that Jehovah would bring his words to them, for the purpose “of convincing them of the true Messiah.”
The future Jews will already have all of the scriptures that Nephi had known, as well as others from after the time that Nephi left Jerusalem. The marvelous work would not be the Torah. That had already been provided, and the Jews had already misunderstood how it foretold the atoning Messiah. The marvelous work would be the Book of Mormon. It is interesting that here it would come to convince the Jews of the Messiah, and the Book of Mormon’s title page would also indicate that it was for the convincing of the “Jew and Gentile that Jesus is the Christ, the Eternal God.”
Nephi repeats the prophecy from the angel, recorded in 1 Nephi 19:8, that the atoning Messiah would come six hundred years from the time Lehi left Jerusalem. As noted in Episode 157, the timing between the time Lehi left Jerusalem to the suggested birth of Christ does not leave us six hundred years. Nevertheless, the Book of Mormon counts down six hundred years. The explanation, as noted in Episode 157, is the use of either the Jewish lunar calendar, or the adoption of the Mesoamerican 360-day calendar. Shortening the years only by those few days over time would yield six hundred of those shorter years.