Simplify the following text for a Grade 10 native English-speaking person.
Original: While in Cambrai he collaborated with Nicolas Grenon on a complete revision of the liturgical musical collection of the cathedral , which included writing an extensive collection of polyphonic music for services .
Simplified: While in Cambrai he worked with Nicolas Grenon on completely renewing the cathedral collection of music . This meant that he had to write a big collection of polyphonic music for services .