In these verses father Lehi explains the role of Satan. In the Garden of Eden, Satan told Eve one truth in order to get her to believe a monstrous lie. For example, he told her if she would partake of the fruit of the tree of knowledge it would make her wise like God. She would know the difference between good from evil. That actually was a divine truth. But then he turned around and repudiated the warning of the Father that if they partook of the fruit they would surely die. Satan said to Eve, "Partake of the fruit. You will not die." And of course this was a lie.
In fact after Adam and Eve partook of the fruit from the tree of knowledge, it not only changed their physical bodies and gave them the ability to discern good from evil like their Heavenly Father but great changes occurred in their physical bodies. The seeds of death began to take effect that would eventually cause them to die, but in their changed condition they were able to have children for the first time. We should notice one other thing before leaving this particular scripture. This is the only place which explains why it was necessary to extend the life span of mankind during the patriarchal period. It was so the first generations would hear the gospel before they died, and as you know, many of them lived to be nearly a thousand years old.