Joseph Fielding Smith

Adam's transgression brought these two deaths: spiritual and temporal--man being banished from the presence of God, and also becoming mortal and subject to all the ills of the flesh. In order that he should be brought back again, there had to be a reparation of the broken law. Justice demanded it.

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. Justice demanded that the law which was broken be repaired. Justice demanded that by the giving of life Adam and his posterity will be brought back into the presence of God. (Doctrines of Salvation, 1:122)