Their main question, in 1 Nephi 22:1, was whether what Isaiah was describing was "spiritual, which shall come to pass according to the spirit and not the flesh". In other words, in today's terms, their question was somewhat loaded. They wanted to know whether it was meant to be figurative or real.
Nephi gently corrects them by saying that because the words of Isaiah were received through the Spirit, that in that sense they were spiritual. They were also temporal (literal) in that they would someday come to pass.
He describes what today we call "the diaspora", or the great scattering of the twelve tribes of Israel such that ten of those tribes were completely lost in the great populations of the earth.
Nephi goes on to explain that it is through the Gentiles that Israel will be gathered back to their ancestral homeland.
Verses 7-9 describe how the Gentiles would found a great nation which would be instrumental in scattering Laman and Lemuel's posterity. Then, the Lord would restore the Gospel through the Gentiles and gather together the remnant of the people left over. In the LDS Church, we understand the fulfillment of this prophecy to be the founding of the United States of America and the various Latin American countries by European nations (what the Jews would consider "Gentiles").
The Lord would use these events as a catalyst for gathering from all parts of the world every living descendant (and deceased, through restored temple ordinances) of the house of Israel, most particularly those of the lost ten tribes.
At the end of the gathering, the Lord will destroy any worldly organizations that rise up to fight against His Gospel and who try to persecute His servants. He will miraculously preserve the righteous during that terrible time. "Wherefore, the righteous need not fear; for thus saith the prophet [Isaiah], they shall be saved, even if it so be as by fire."
People who read the Bible today often ask the question "In what way will Satan be bound when Christ comes?" While it is tempting to think of Satan, the individual, tied up with ropes so he can't bother us anymore, he is a spirit with free will and cannot be contained in that way, even by God, who will never force anyone to do anything against their will.
Rather, the Book of Mormon clearly teaches that because of the faith in Christ of those righteous people remaining after the destruction, they will be righteous (Christ's atonement covering their sins) "And because of the righteousness of his people, Satan has no power; wherefore, he cannot be loosed for the space of many years; for he hath no power over the hearts of the people, for they dwell in righteousness, and the Holy One of Israel reigneth."
Quite literally, they will not be tempted by Satan because they will not have a desire to sin because of their faith in Christ. They will know where such things lead, based on the experience of witnessing the destruction of the world, and will instead reject temptations when they come and choose to obey only righteous principles.
The overall message Nephi has for his brothers is to repent so that they can be counted among the righteous when the Lord comes the second time at the end of the world.
30 Wherefore, my brethren, I would that ye should consider that the things which have been written upon the plates of brass are true; and they testify that a man must be obedient to the commandments of God.