Instruments have divided Christendom since their introduction into worship. They were considered a Catholic innovation, not widely practiced until the 18th century, and were opposed vigorously in worship by a number of Protestant Reformers, including Martin Luther (1483–1546), Ulrich Zwingli, John Calvin (1509–1564) and John Wesley (1703–1791). Alexander Campbell referred to the use of an instrument in worship as "a cow bell in a concert". In Sir Walter Scott's The Heart of Midlothian, the heroine, Jeanie Deans, a Scottish Presbyterian, writes to her father about the church situation she has found in England (bold added):
What did Martin Luther mention about using instruments during church worship?