Alma is referring here to Adam and Eve’s valiant decision to eat the fruit offered to them in the Garden of Eden. Without it, they would have been “forever miserable” because they would have had no opportunity to improve their stagnant situation and childlike state (2 Nephi 2:21). In Mormonism, spiritual progress is paramount, both in this life (the preparatory state Alma speaks of) and in the life to come.