The miracle of the preservation of the Ammonite sons is noticed by all the army. There have been a thousand casualties, but none of them among the Ammonites. It was certainly not because they were spared direct confrontation, for they were clearly in the thick of the fighting. Nevertheless, they were preserved.
Historical: A note should be made on the numbers of men lost in this battle. We know that Helaman could have easily fielded an army of eight thousand men. He had his two thousand, and the six thousand who had come from Zarahemla. That does not count the remainder of the men of the army of Antipus, which surely exceeded Helaman’s two thousand. As a rough guess, we may suppose that there were eight thousand Nephites defending the field from the attacking Lamanites. Out of eight thousand there are only a thousand deaths. Why is it that the Nephites believed that they were losing the battle?
The nature of ancient warfare was such that the attrition of men was not simply through death, but also through injury. Helaman had those in his charge who were ineffective in battle because they had fainted. While still alive, they were nevertheless non-combatants. Similarly, some of the injuries may have been enough to remove a warrior from combat. One who had received injuries to his arms that did not allow him to raise a weapon might still be alive, but were ineffective. Battles typically included far greater numbers of wounded that dead. Thus a thousand dead did not indicate the real weakness of the position of the army. The weakness came as well from those who were wounded and therefore unable to continue the combat.
The miracle of the Ammonites was not in their complete preservation, but in their ultimate preservation. They did not escape injury, but even through their injuries they did escape death. The complete absence of loss of life among them was miraculous, and Helaman and the army focused on that part of the miracle.
Spiritual: The lesson of the Ammonite warriors is certainly one of the effectiveness of faith, but it should also teach us that ultimate salvation and absence from pain are not the same promise. We too are promised salvation upon our faith, but we are not promised that we will not be injured along the way. For some it is a physical injury, for some it is a spiritual one. In all cases, the promise of our eternal reward does not prevent us from all of the bumps in the road that life throws at us. Even though the promises to the Ammonites were explicitly fulfilled, we should not extrapolate their preservation unduly. They had a specific promise given as a corollary to the Nephite foundational promise, that they would be preserved through their righteousness. This became a specific promise for them. While we have the same ultimate promise, the promise is more spiritual and than literal, and there are many worthy young men and women who have lost their lives, in spite of their righteousness. For most of us, the fulfillment of this promise may not come in the mortal life, but is guaranteed to us in the eternal.