Lehi provides an important discourse on the nature of salvation, but it is densely worded. First, Lehi declares that “men are instructed sufficiently that they know good from evil.” That is a critical foundation of God’s plan of redemption. If humankind were unable to tell the difference between good and evil, no one could be held accountable for their choice of either. Thus, it is absolutely required that from the very beginning there be an eternal assurance that it was possible to make the distinction.
The experience of the world tells us that what different cultures in different times have considered good or evil becomes flexible around the edges of those concepts, but there are some human universals where all cultures instinctively understand, for example, that murder and incest are to be forbidden. Nevertheless, even when cultures define some things differently, each person has the opportunity to understand good and evil according to their culture first, and some to add to their understanding the definitions that come from God rather than from man. In all cases, the Spirit of Christ can act as a testator to whether anything is right or wrong. The Spirit of Christ becomes that assurance that we are capable of discerning good from evil.
Lehi explains that we have a law given, but “by the law no flesh is justified.” That language references Paul when he spoke of the same principles (see Romans 3:20). On top of any culturally defined right and wrong, God has provided a law to define the actions that He defines as right or wrong. Thus, there is a way to be judged according to a law higher than cultural law. However, obedience to the law alone does not save.
When Lehi says that “by the temporal law they were cut off,” he refers to the fact that no human is perfect. That imperfect ability to follow all of God’s law requires, according to His justice, that we be cut off from His presence.
The only solution to this potential disaster is through the Atonement of the Holy Messiah, or Jehovah, who will come to earth to enact our redemption.