The function of “and it came to pass” in the Book of Mormon is to move narrated events from one event to the next. Book of Mormon writers were not writing in English, and wrote long before ideas of punctuation had been invented and inserted into texts. The function of punctuation is to replicate some of the pauses we use in speech that allow our listeners to make sense of what we are saying. Rather than punctuation, Book of Mormon writers use linguistic markers that let their readers understand what is occurring in the text. Thus, there are many types of repeated phrases, and they often function as substitutes for punctuation. Even the ubiquitous “and”, which accompanies the majority of sentences, serves to link ideas, and to create connections where there are no punctuation marks.
In this case, the “and it came to pass” notes that Lehi’s dream occurs at some time after the previous events. That is reinforced when Nephi says that this happened after his father tarried in the wilderness. We don’t know how long between events this was, and marking the specifics of the timing wasn’t what Nephi was interested in. Nephi wants to record his father’s dream. Certainly, he does this because it was important, but the dream is included more for what it meant for Nephi than what it meant to Lehi.
Lehi summarizes the meaning that he understands of the dream in verses 3 and 4. He has reason to rejoice because of Nephi and Sam, but reason to fear exceedingly because of Laman and Lemuel. The point of Lehi’s dream is in the specific sons who partake of the fruit. Nephi’s version of the same vision will have a dramatically expanded significance.