Nephi appears to have written his second book many years after completing the first book of Nephi. During the passing years he has had time to carefully study the book of Isaiah and compare his own vision with the things which Isaiah saw. But for the sake of continuity, Nephi now goes back to the most important event following the closing of the first book of Nephi. He wants to tell us about the end of Lehi's life and the death-bed messages which he gave to his sons.
As nearly as we can tell, Lehi's 13th revelation was concerning the destruction of Jerusalem by the Babylonians in 587 B.C., which was 13 years after Lehi left Jerusalem. Lehi wants his sons to know how close they came to being destroyed and how fortunate they were to have arrived in the promised land in spite of their extremely miserable rebellions off and on ever since they left Jerusalem.