Complex sentence: The libretto, written by Pfitzner himself, is based on a legend about the Renaissance composer Giovanni Palestrina, who saved the art of contrapuntal music (polyphony) for the Church in the sixteenth century, through his composition of the "Missa Papae Marcelli".
Split into simpler sentences: The libretto, written by Pfitzner himself, is based on a legend about the Renaissance composer Giovanni Palestrina. The plot describes how he saved the art of contrapuntal music (polyphony) for the Church in the sixteenth century, through his composition of the "Missa Papae Marcelli".