Alma calls for repentance. He has no joy in the doom he has forecast, and he continues to appeal to the Ammonihahites to do the one thing that will prevent the predicted temporal and spiritual death. He asks them to repent.
Alma mentions "these his second commandments." To understand to what Alma refers, we need to remember that he has begun with the story of the Garden of Eden. The first commandments were given at the beginning of Eden. "These his second commandments" are those that were given after the Fall, so that mankind could learn how to repent and chose good over evil.
Textual: This chapter is broken in the middle of a paragraph of the 1830 edition. We should understand that there is no conceptual stop here. Alma continued his discourse without significant pause.