Preservation by Faith - Alma 57:26

...according to the goodness of God, and to our great astonishment, and also the joy of our whole army, there was not one soul of them who did perish; ... And now, their preservation was astonishing to our whole army, yea, that they should be spared while there was a thousand of our brethren who were slain. And we do justly ascribe it to the miraculous power of God, because of their exceeding faith in that which they had been taught to believe—that there was a just God, and whosoever did not doubt, that they should be preserved by his marvelous power.

This is the story of the "stripling warriors", so-called because of their youth. They were sent to war to defend their fathers at a young age. Their fathers had all made solemn promises to God of non-violence, but when they became the object of their enemies' hatred, the Nephite army stepped in to protect them. Seeing the Nephite's suffering in their behalf, against an enemy against which they were outnumbered, they were about to break their oath, but the Nephites wouldn't have it. Instead, the younger generation who had never made the oath were sent to war.

The Nephite leaders did not intend to use the youths on the front lines out of respect to their fathers, but during several campaigns, the youths stepped forward and fought "undaunted", because "they did not fear death", and were the means of saving the entire army on many occasions.

These youths were raised on true principles by their parents, and likely had a hard life, but were full of faith. And because of their faith in promises received, were continuously preserved in battle. In their faith, there was no room for doubt - an invariant that must be met for faith, since faith and doubt cannot exist in the soul at the same time.