Mit Brennender Sorge was a letter written by the Pope a long time ago. He wrote it to tell people in Germany that their government was doing things that were not okay. The Pope told everyone to remember that everyone is equal and should be treated with respect, no matter what. He also said that it was important to follow God's rules and be good to each other. The letter was important because it helped people remember that being kind and fair is always the right thing to do, no matter what the government says.