Medieval nobles were horrible, violent people. They would beat peasants for fun and trample crops of poor people during their jousting matches. They burned peasant homes for sport. Why? Because they could. They were the warrior class and had the weapons.
In the early middle ages, a knight was someone who had money to buy armor and weapons. Eventually, knights came to be considered a lower tier of the nobility, and titles became hereditary. But they were still usually uncouth. They mistreated women and exhibited terrible dining manners.
The Catholic church tried to remedy the situation with two programs, the Peace of God and the Truce of God. At the Council of Charroux, the Peace of God was proclaimed in 989. It called for protection of church property and clerics and of cropland. The Truce of God was proclaimed in 1027, and called for limits on which days the nobility could engage in violence.
Peace and Truce of God may have been temporarily useful in some cases, but overall is considered to have been a failure. Peace & Truce tried to cover too many people on too many topics, as mission creep added in multiple rules (such as treatment of orphans, widows, and animals etc.). But it would have been unsuccessful anyway. Nobles don’t like to be told what they cannot do. Also, the rule books were written in Latin, and most nobles could barely read their local languages.
Peace & Truce 2.0 was much more successful. It was called Chivalry. This was a system designed to encourage nobles, especially knights, from mistreating everyone. It was successful because (1) it was written in local languages, (2) it told them things they could do, rather than not do (romance, etc.) and (3) it employed stories.
Most knights forgot they weren’t allowed to kill peasants on Thursdays. But they remembered the tales of Lancelot.
Stories should offer opportunity
Instead of saying “you can’t rape villagers on Tuesdays,” the program offered the opportunity to be heroes. They could rescue villagers from dragons. Your stories should suggest more opportunity than punishment.
Stories should be in the language of the hearer
Jesus used stories of farmers planting and harvesting. It was effective for millenia. But now, people think grocery stores magically manufacture food. Use the words your people understand. Use the images they understand.
Stories should be entertaining enough to be memorable
People remember the frightening dragons and the beautiful Guinevere. People don’t remember “sales targets in the eastern region will increase by 2.43%” phrases.
Stories should make the lessons clear
After the chivalric program was implemented and knights read the stories, they knew they should treat women well, eat politely at the dinner table, and help people instead of hurting them. It was clear. If you want to be like Lancelot, be good.