Alma 4:3

and so great was their afflictions, that every soul had cause to mourn; and they believed that it was the judgments of God sent upon them, because of their wickedness and their abominations; therefore they were awakened to a remembrance of their duty.

Their troubles were so great that everyone was sad. They believed that God was punishing them because of their sins. So they remembered what they should be doing.

The loss was so crushing that everyone had reason to mourn. They believed God’s judgment had fallen on them because of their sins and wickedness, and this woke them up to their responsibilities.