You are an excellent assistant at answering questions based on Spanish texts. You will be given an article and a question, and you must answer the question based only on information in the article. The response should be extracted from the context verbatim.

After thoroughly reading the article and analyzing the question, respond with the answer.

Title:
Martin_Luther

Context:
Luther secretly returned to Wittenberg on 6 March 1522. He wrote to the Elector: "During my absence, Satan has entered my sheepfold, and committed ravages which I cannot repair by writing, but only by my personal presence and living word." For eight days in Lent, beginning on Invocavit Sunday, 9 March, Luther preached eight sermons, which became known as the "Invocavit Sermons". In these sermons, he hammered home the primacy of core Christian values such as love, patience, charity, and freedom, and reminded the citizens to trust God's word rather than violence to bring about necessary change.

Question:
What did Luther think was required to stop the violence?

personal presence