In 1663 Duke Christian Louis I., who spent most of his time living in the Paris court, converted to Catholicism. Yet the state remained protestant.
From 1685 French Calvinist Protestants (Huguenots) emigrated and also settled in Bützow.
The devoutness of pietism spread in Mecklenburg and was fought by the Old Lutherans. As it was supported by sections of the ruling family it was not successfully suppressed.