Complex sentence: The Protestant reformer Martin Luther had emphasised the importance of singing hymns in church services and at home, and had written many hymns, including "Mit Fried und Freud ich fahr dahin".
Split into simpler sentences: The Protestant reformer Martin Luther had emphasised the importance of singing hymns in church services and at home. He had written many hymns, including "Mit Fried und Freud ich fahr dahin".