In explaining his gospel to the Nephites of about A.D. 34, the resurrected Jesus Christ also explained why it was necessary for him to come here upon this earth and atone for sin and provide for the resurrection. Concerning this dual contribution of the Savior and Redeemer of mankind, B. H. Roberts has written:
The effect of Adam’s transgression was to destroy the harmony of things in this world. As a consequence of his fall man is banished from the presence of God—a spiritual death takes place and man becomes sensual, devilish, unholy, is cursed, we say, with a strong inclination to sinfulness. Man is also made subject to a temporal death, a separation of the spirit and body. Much might have been gained by this union of his spirit with his body of flesh and bone could it have been immortal, but that is now lost, by this temporal death, this separation of spirit and body. These conditions would have remained eternally fixed as the result of the operation of law—inexorable law, called “the justice of God,” admitting of nothing else; for the law was given to eternal beings and by them violated, and man is left in the grasp of eternal justice, with all its consequences upon his head and the head of his progeny. And the justice of the law admitted the conditions, admitted that the penalties affixed should be effective, but this is justice—stern, unrelenting justice; justice untempered by mercy. But mercy must in some way be made to reach man, yet in a way also that will not destroy justice; for justice must be maintained, else all is confusion—ruin. If justice be destroyed—if justice be not maintained—“God will cease to be God.” Hence mercy may not be introduced into the divine economy of this world without a vindication of the broken law by some means or other, for divine laws as well as human ones are mere nullities if their penalties be not in force.
The penalty of the law then, transgressed by Adam, must be executed, or else an adequate atonement must be made for man’s transgression. This the work of the Christ. He makes the atonement. He comes to earth and assumes responsibility for this transgression of law, and gathers up into his own soul all the suffering due to the transgression of the law by Adam. All the suffering due to individual transgression of law—the direct consequences of the original transgression—from Adam to the end of the world.
The burden of us all is laid upon him. He will bear our griefs and carry our sorrows. He will be wounded for our transgressions, and be bruised for our iniquities. The chastisement of our peace will be upon him; on him is laid the iniquity of us all; by his stripes shall we be healed. That is to say, having gathered into himself all the suffering and sorrows due to all the sinning that shall be in the world, he is able to dictate the terms upon which man may lay hold of mercy—by which mercy may heal his wounds—and these terms he names in the conditions of the gospel, the acceptance of which brings complete redemption. The Christ brings to pass the resurrection of the dead. The spirit and the body are eternally reunited; the temporal death—one of the effects of Adam’s transgression—is overcome. There is no more physical death; the “soul”—the eternally united spirit and body are now to be immortal as spirit alone before was immortal. The man so immortal is brought back into the presence of God, and if he has accepted the terms of the gospel by which he is redeemed from the effects of his own, as well as from Adam’s transgression, his spiritual death is ended, and henceforth he may be spiritually immortal as well as physically immortal—eternally with God in an atmosphere of righteousness—the spiritual death is overcome.
Such I make out to be the Book of Mormon doctrine of the atonement, and the redemption of man through the gospel. (New Witnesses for God, 3:216-18.)
For additional review on the important subject of the atonement, re-read the materials following 2 Nephi 9:6-9 and Mosiah 3:15-27.