Lehi alludes to an event not otherwise mentioned in Nephi's account. Clearly Jacob had a similar epiphany to that of Nephi, where he was able to know of himself though a vision/visitation the mission of the Savior. The phrase that Lehi uses is "beheld in thy youth his glory" is suggestive that either a personage of glory attended to Jacob, or that his vision laid out the glory of the Savior's mission. When Lehi also suggests that Jacob is blessed in the same way as those who will receive Christ's ministrations in the flesh, it appears that it may have been Christ himself who visited Jacob, though this is not necessarily required in the way the text is written.
The point of Lehi's phrasing, however, is not to dwell on Jacob, but rather on the Savior and his mission, so he moves without further emphasis on Jacob's experience to the real message - Christ. His next phrasing is interesting from a literary perspective as it forms the basis of the shift in topic: "for the Spirit is the same, yesterday, today, and forever. And the way is prepared from the fall of man, and salvation is free." The object of stating that the Spirit is the same yesterday, today, and forever is most directly related to Lehi's comment about Jacob's blessing being the same as those who will in the future speak with the Savior incarnate. While that is the issue, the eternal nature of the spirit also allows Lehi to shift a focus from forward in time to backward in time. The next phrase returns to "the beginning" and couches the rest of his discourse in the events established before and after the fall of man. His preliminary indication of his topic is that there is a "way. . . prepared from the fall of man" and that this prepared way is free to all men.