At the end of the ten-year span of peace, the king of the Lamanites had sent a letter warning that the treaty was over, and that fighting would resume. Mormon led his people in two successful battles, one in the 361st year, in the Land of Desolation (Mormon 3:7), and another in the 362nd year (v. 8), in which they “did slay a great number of them.” However, it becomes clear in Mormon 3:9 that the Nephites became proud and boastful because of their success. Not only were they interested in revenge, but they even swore before the heavens that they would avenge themselves of the blood of their brethren.
The war, to the Nephites, became an offensive action. It is quite possible that their choices were based partly on a desire to step into a position of advantage, and win, but their motivation and trust in themselves precluded the help of the Lord.
Primarily, they wrongly became avengers of blood. Avengers of blood were part of the Law of Moses. If one had a brother or first-level relative murdered, there was an obligation under the Law of Moses to act as what was called the redeemer of blood, or go-el hadam, and to even the score. They may have been using this old law to say that God would justify their thirst for revenge. Though this was 330 years after Christ appeared, there were lingering questions about which parts of the Law of Moses were supposed to have been discontinued and which were still applicable. Possibly, they were falling back into old customs. For example, in Moroni 8, which was an “epistle of my father Mormon, written to me, Moroni; and it was written unto me soon after my calling to the ministry,” it was noted that the law of circumcision was done away in Christ. This sort of confusion also happened in Jerusalem among a number of early Christian converts.
It was not always clear which parts of the Law of Moses were to be done away with and which were not. For example, the law of the Sabbath is still followed, but other parts of the Law of Moses are not. Prophetic instruction was required to differentiate between those parts to be retained and those parts to be discontinued. Thus, although one may understand where they might have acquired their idea, they were still incorrect.
They were warned that exacting revenge was sinful, but they ignored the prophet, Mormon. One may ask whether seeking revenge is a common part of life today. In what ways do even Latter-day Saints “get back” at people in our society? It happens at a national level; it happens in the lives of individuals. Road rage is a modern example of vengeful behavior. Holding grudges or considering getting even with someone are common failings.
Mormon retired at the age of 53 because he could no longer stand at the head of the vengeful and bitter Nephites who would neither hear his cry for repentance nor cease being avengers. In Mormon 3:11–16, he announced that he would stand down. For what it may or may not have been worth in Mormon’s day, the mandatory retirement age of priests under the Law of Moses was 50 (see Numbers 8:25). Mormon was called back into service and accepted the role of leader again at the very end of his life, 20 years later.