When the people were spared in a miraculous way, they were all converted. Notice the impact of their belief in the prophets (read for us scripture and pronouncements of living prophets and apostles):
3 Therefore they did forsake all their sins, and their abominations, and their whoredoms, and did serve God with all diligence day and night.
Elder Boyd K. Packer said: “True doctrine, understood, changes attitudes and behavior. The study of the doctrines of the gospel will improve behavior quicker than a study of behavior will improve behavior” (in Conference Report, Oct. 1986, 20; or Ensign, Nov. 1986, 17). No worldly ideas or principles have this power. No spellbinding lectures or entertaining presentations can touch individuals so profoundly that they turn their hearts to Christ. Centering our teaching on the truths of the gospel is the only way we can become instruments in God’s hands to help instill the faith that will lead others to repent and come unto Him.
The teaching of doctrine protects us against spiritual waywardness. It can call us back when we go astray.
“10: The Power of the Word,” Teaching, No Greater Call: A Resource Guide for Gospel Teaching, 50