Alma Ch28

There is a battle and the Lamanites lose, but both sides lost plenty. All that were slain will either consigned to endless woe if wicked or attain never-ending happiness if righteous.
The armies of the Lamanites had followed the people of Ammon and attacked after they had settled in Jershon with the result of a tremendous battle in which tens of thousands of the Lamanites were slain (v1-2). There were also many of the Nephites who were slain in the fight but they did win and mourned for their lost brethren after driving the enemy out (v3-5). It caused everyone to mourn for brother, father, son, or whoever died and many fasted and prayed, and this is how the 15th year ended (v6-7).
From now one we are going to read about all the sufferings, journeyings, afflictions, incomprehensible joys, contentions, and wars that happen to both the Nephites and Lamanites that are told from the account of Alma and his brethren (v8-9). It started with this battle that caused many deaths, but not all who died have reason to fear like the wicked who will have endless woe in the after life (v10-11). Those who had been righteous will be raised to the hand of God and be happy forever (v12).
Through all of this pain and mourning because of battle we learn how wicked man can become if they are ensnared by the devil (v13). But on the flip side of that, we have the righteousness of diligent men who serve the Lord like the sons of Mosiah (v14). There is both sorrow and rejoicing in this world but our goal is to end up able to rejoice for what we have accomplished in this life.