In four verses - D&C 29:40-43 - is a summation of Adam's transgression, his banishment from the Garden of Eden and presence of the Lord, and the promise of redemption through the atonement of Jesus Christ.
In Gospel Doctrine is this teaching by President Joseph F. Smith:"When Adam, our first parent, partook of the forbidden fruit, transgressed the law of God, and became subject unto Satan, he was banished from the presence of God, and was thrust into outer spiritual darkness. This was the first death.
"Yet living, he [AdamT was dead - dead to God, dead to light and truth, dead spiritually; cast out from the presence of God; communication between the Father and the Son was cut off. He was absolutely thrust out from the presence of God as was Satan and the hosts that followed him. That was spiritual death.
"But the Lord said that He would not suffer Adam nor his posterity to come to the temporal death until they should have means by which they might be redeemed from the first death, which is spiritual. Therefore angels were sent unto Adam, who taught him the gospel, and revealed to him the principle by which he could be redeemed from the first death, and be brought back from banishment and outer darkness into the marvelous light of the gospel. He was taught faith, repentance, and baptism for the remission of sins, in the name of Jesus Christ, who should come in the meridian of time and take away the sin of the world, and was thus given a chance to be redeemed from the spiritual death before he should die the temporal death.
"Now, all the world today, I am sorry to say, with the exception of a handful of people who have obeyed the new and everlasting covenant, are suffering this spiritual death. They are cast out from the presence of God. They are without God, without gospel truth, and without the power of redemption; for they know not God nor His gospel. In order that they may be redeemed and saved from the spiritual death which has spread over the world like a pall, they must repent of their sins, and be baptized by one having authority, for the remission of their sins, that they may be born of God. That is why we want these young men to go out into the world to preach the gospel."