Let me explain why.

We read in verse 12 that King Benjamin "had somewhat of contentions among his own people." This contention come from two places:
- from outside the kingdom - the armies of the Lamanites came down to battle (vs. 13)
- from inside his kingdom with "false prophets, and false preachers and teachers among the people" (vs. 16).
King Benjamin loved his people and wanted their safety, both physically and spiritually, so he had to end the contentions. He was successful and we read in verse 18 that "by laboring with all the might of his body and the faculty of his whole soul did once more establish peace in the land."
How did he fight the contentions from both the outside and inside of his kingdom?
Against his outside enemies, the Lamanites, we read that he "gathered together his armies, and he did stand against them; and he did fight with the strength of his own arm. And in the strength of the Lord they did contend against their enemies." (vs. 13-14)
Against the internal enemies seeking to destroy them spiritually, "with the assistance of the holy prophets who were among his people, [the false prophets, and false preachers and teachers] mouths had been shut, and they punished according to their crimes" (vs. 15-16)
What allowed King Benjamin to accomplish these things? In verse 17 we read that King Benjamin was a "holy man, and he did reign over his people in righteousness; and there were many holy men in the land, and they did speak the word of God with power and with authority; and they did use much sharpness because of the stiffneckedness of the people"
So how does this apply to me and my home?
We also have enemies on the outside trying to harm our families spiritually. Through scripture and the words of the prophets we know who the adversary is and what he is trying to do. Elder Marion G. Romney said, "We need not be, and we must not be, deceived by the sophistries of men concerning the reality of Satan. There is a personal devil, and we had better believe it. He and a countless host of followers, seen and unseen, are exercising a controlling influence upon men and their affairs in our world today." (link here)
His goal is to “destroy the souls of men.” (D&C 10:27.)
“… he persuadeth no man to do good, no, not one; neither do his angels; neither do they who subject themselves unto him.” (Moro. 7:17.)
At the last supper just prior to his ordeal in Gethsemane, Jesus warned Peter: “Simon, Simon, … Satan hath desired to have you, that he may sift you as wheat.” (Luke 22:31.)
How do we take what King Benjamin taught us about outside enemies to fight the adversary today? We FORTIFY AND FIGHT!

We also fight against contentions inside our homes. In my house those things look like: yelling, arguing, bullying, teasing, sarcasm, insults, speaking unkindly and basically anything that tears us apart instead of bringing us together as a family.
We can replace those behaviors with: soft voices, keeping calm, obeying rules, giving service, treating others the way we want to be treated, forgiveness, apologizing and respect.
What kind of people do we need to be to accomplish this?
We need to be like King Benjamin, righteous and holy, speaking the word of God with power and authority. Sometimes as parents we, like King Benjamin, need to also use sharpness. Doctrine and Covenants 121:43 tells us how this should be done, "Reproving betimes with sharpness, when moved upon by the Holy Ghost; and then showing forth afterwards an increase of love toward him whom thou hast reproved, lest he esteem thee to be his enemy."
In Mosiah 1:1 we read the end of the story. "And now there was no more contention in all the land, among all the people who belonged to king Benjamin, so that king Benjamin had continual peace all the remainder of his days."
We must be like King Benjamin and "laboring with all the might of [our] body and the faculty of [our] whole soul" against contentions inside and outside our homes and by following the example of King Benjamin, we will be successful.