I read a commentary on this chapter that brought up a point I haven't considered before. The point was that those who read the Book of Mormon have an expanded knowledge of these Isaiah chapters that any who read the Bible would benefit from. I'm sure all Bible readers find the language in the book of Isaiah sort of hard to follow and would benefit from these chapters where Jacob is trying to explain Isaiah to his people. I would be fascinated to hear what a Bible Study group thought of these Book of Mormon chapters "overlap" with the Bible.
These next two quotes really sum up why death is important but why it would stop our eternal progress if the Atonement was not fulfilled.
“Death is just as important in the welfare of man as is birth. There is no greater blessing that can come than the blessing of birth. One third of the hosts of heaven, because of rebellion, were denied that privilege, and hence they have no bodies of flesh and bones, that great gift of God. “But who would like to live forever in this mundane world, filled with pain, decay, sorrow, and tribulation, and grow old and infirm and yet have to remain with all the vicissitudes of mortality? I think all of us would come to the conclusion, if that proposition were placed before us, that we would not like to have it. We would reject it. We would not want life of that nature. Life here in this world is short of necessity, and yet all that is required may be accomplished, but death is just as important in the plan of salvation as birth is. We have to die—it is essential—and death comes into the world ‘to fulfil the merciful plan of the great Creator.’” (Joseph Fielding Smith, Doctrines of Salvation, 1:116).
“The fall brought death. That is not a desirable condition. We do not want to be banished from the presence of God. We do not want to be subject forever to mortal conditions. We do not want to die and have our bodies turn to dust, and the spirits that possess these bodies by right, turned over to the realm of Satan and become subject to him. “But that was the condition; and if Christ had not come as the atoning sacrifice, in demand of the law of justice, to repair or to atone or to redeem us from the condition that Adam found himself in, and that we find ourselves in; then mortal death would have come; the body would have gone back to the dust from where it came; the spirit would have gone into the realms of Satan’s domain, and have been subject to him forever” (Smith, Doctrines of Salvation, 1:122).