Here is a highly significant verse. There are two things in Nephi's vision he cannot tell the people. He cannot tell them in advance of the changes that will come with Christ's ministry in the meridian of time, and secondly he cannot tell them what will happen to the Saints of the latter days when America is cleansed. This second secret is reserved for the Apostle John to disclose when he writes his prophetic record. You will recalled how this restriction was put on Nephi back in 1 Nephi 14:25-27.
One of the trials of life is to know a thrilling secret you can't tell anybody. So Nephi says, "I am left to mourn because of the unbelief ... of men for they will not search knowledge." Or as Elder Widtsoe would say, "They lacked spiritual curiosity. They are not asking questions."