For the next twenty years, Praetorius served as chamber organist and eventually court music director for Duke Julius. Besides playing organ in the chapel, he arranged for music at meals and recreation, composed pieces for festivals, and taught music to the duke’s children. While in Wolfenbuttel, he also met and married Anna Wernighof, with whom he had two sons.

Praetorius treasured the organ as an instrument that aided the responsive nature of the liturgy. “It is a very lovely and pleasant thing to hear,” he said, “when the entire assembly joins in together with the choir and organ like this, and shows and portrays to some extent what it’s going to be like in heaven when all the dear angels and saints of God intone and take up the Sanctus, Sanctus, Sanctus and Gloria in Excelsis Deo.” Praetorius knew how to build and maintain organs, and he wrote his own manual on organ construction and repair.

Praetorius’s strong Lutheran confession is evident throughout his compositions. He published fifteen installments of sacred music, titled Musae Sionae or Muses of Zion, in which he modified Latin works to be doctrinally sound and arranged an abundance of Lutheran hymns. He wrote for various numbers of voices, so that choirs of any size could use his work. He carefully chose which phrases to repeat in a given piece, depending on which theological point should be emphasized. Even in his secular work, such as the dances in his collection called Terpsichore, Praetoruis’s design was to give listeners enjoyment and rest with decency, separate from the music of pagan worship.