This a classic example of how the prayer of a righteous man, coupled with the faith of the Saints, can accomplish great things (see James 5:16).
“The Lord Hath Heard the Prayers of His People”
Sixth, the prayers of the righteous cannot go unheard. Alma the Elder and Mosiah were both men of great faith who no doubt implored the heavens night and day with a plea of help to save their wayward sons. Nor did they pray alone, for their pleadings were joined by those of all the faithful of the Church in and around Zarahemla.