In chapter 40, verses 11-15 and 21, Alma teaches the differences between paradise and spirit prison. Essentially, Paradise is a state of happiness, versus a state of misery with weeping and wailing.
In chapter 42, Alma teaches why we must have both justice and mercy:
14 And thus we see that all mankind were fallen, and they were in the grasp of justice; yea, the justice of God, which consigned them forever to be cut off from his presence.
15 And now, the plan of mercy could not be brought about except an atonement should be made; therefore God himself atoneth for the sins of the world, to bring about the plan of mercy, to appease the demands of justice, that God might be a perfect, just God, and a merciful God also.
And that's what you need to know for tomorrow's Sunday School Lesson.