In this section, Lehi becomes more specific. After embedding the principle of opposition (and action) in the very creation of the earth, he now explains that principle’s implementation in our mortal circumstances. Mortality begins in the Garden of Eden, where the conditions of opposition and action were set up.
Lehi establishes the two trees as opposites in the garden, thus making the garden the microcosm of the entire creation. Even though all creation has required opposition, here that argument focuses on one event, with the two trees symbolizing all such choices. (See “Excursus: Understanding the Symbols of the Trees in the Garden,” following Alma 12.)
Lehi parallels the two trees (forbidden fruit/tree of life), followed by two attributes (sweet/bitter). While conceptually we would associate the forbidden fruit with bitterness, the parallel associates forbiddenness with sweetness and the tree of life with bitterness. Why would Lehi thus reverse our expectations? Because eating the forbidden fruit generated the conditions of opposition, thus creating Lehi’s bitter/sweet dichotomy. The sweet fruit was truly tempting (as was the promise to become as the gods). The process of agency by which we become as the gods is often all too bitter.