The last episode examined verse 4 as part of the transition to Lehi’s discussion of the coming Messiah. That verse is repeated here because the 600-year prophecy is both important to the Book of Mormon, and a difficulty that needs to be examined.
The first year of the reign of Zedekiah was 597 B.C. Lehi was called as a prophet during that year, but likely did not leave Jerusalem until later. Randall Spackman has calculated the probable departure as 587 B.C., or soon before the Babylonian destruction of Jerusalem. Those are firm dates.
Scholars place the birth of Christ around 4–6 B.C. In between we have to fit a 600-year prophecy into what is clearly less than 600 years.
The first question is whether or not the 600 year prophecy was approximate or precise. The Book of Mormon clearly answers that by counting down the years, and marking 600 years. This must be calculated across different starting dates for the Nephite calendar, but when those correlations are made, we have 600 years. The answer to the question of precision is that it is precise.
Now, the obvious question is how can we have 600 years in less than 600 years? The answer is that while it is obvious to the modern world that we should count the year as one revolution of the earth around the sun, that is not the only way a year can be defined. At the time Lehi left Jerusalem, the Israelites used a lunar calendar, which has fewer days than a solar calendar.
If we understand that the Nephites arrived in Mesoamerica, there was also a calendar in use that had a number of days that was closer to the lunar year than the solar. If we calculated the lunar years (without adding the extra days to reconnect to the solar calendar), then we have 600 years. In this case, the Book of Mormon is seemingly wrong in the 600 years, but it is wrong in just the precise way as to actually be accurate.