1 Nephi 3:18

For behold, they have rejected the words of the prophets—Wherefore if my father should dwell in the land after that he hath been commanded to flee out of the land, behold he would also perish. Wherefore it must needs be that he flee out of the land.

They said no to the words of God’s prophets. So if my father stayed in the land after God told him to leave, he would die too. That’s why he had to leave the land.

'They rejected the prophets' warnings. If Father had stayed after God told him to flee, he would have died with them. He had to leave.'