In verse 12, Nephi mentions that he had already spoken of the convincing of the Jews that Jesus is the very Christ. He is referring to 2 Nephi 25:18 where he specifically said that his words would be “for the purpose of convincing them of the true Messiah.” As the coming Messiah, Jesus would manifest “himself unto all those who believe in him,” and would work “mighty miracles, signs and wonders.” Those would be evidence that he was truly the Messiah.
With that purpose in mind, Nephi moves to the next phase of his vision, which is the time when the convincing of the Jew and Gentile would begin to come to pass. From Nephi’s perspective, that will be the last days. From our perspective, it is the coming forth of the Book of Mormon.