Complex sentence: This is the first time in the film that Luther is confronted about his actions, and he defends himself by affirming that he did see a vision in the thunderstorm that moved him to make a promise to St. Anne to become a monk.
Split into simpler sentences: This is the first time in the film that Luther is confronted. Luther defends himself by affirming that he did see a vision in the thunderstorm that moved him to make a promise to St. Anne to become a monk.