The plan of God cannot be completed while humanity exercises choice, and humanity could be eternally condemned for that choice. Repentance is one of the greatest gifts of God, but could not be available unless there was a reconciliation between justice and mercy. This is where Lehi reinforces the sacrificial mission of the mortal Messiah. He does not state it explicitly, but it is an underlying theme from the beginning of this discourse. Israel already understood that a sacrifice could redeem humanity from sin. The Messiah, who would come in Lehi’s future and our past, provided that atoning sacrifice.
Thus, the fitting conclusion to the story of the creation of God’s plan for his children lies in the ability of the Messiah to make it effective, to reconcile the imbalance of the Trees. Only through the Atonement could God’s children have the chance to have the desired combination of eternal life and Godly knowledge of good and evil.
Thus, in Lehi’s words, “men are free according to the flesh.” That is, in mortality, we have the agency to choose. We can choose good or evil, and eternal life or eternal death. Lehi personifies the choice as one between God and the fallen angel. Lehi used the Mediator, or the Messiah, as the representative for God, and modern readers should remember that Lehi understood Jehovah to be his God, and to be the very one who would condescend to become mortal and to bring about the Atonement.