In The Whole Church Sings (41), Robin Leaver summarizes Andreas Karlstadt’s 53 theses against Gregorian chant (1521):
“It is a consecutive tirade, not particularly well-organized, against all forms of liturgical music then current, not just Gregorian chant, which is dismissed as the ‘mumblings of the unlearned’ (Thesis 31). Chant sung in the Mass and daily Office ‘withdraws the mind from God’ (Thesis 7) and is ‘nothing other than a noisy din’ (Thesis 14). Organs and other musical instruments are for theaters (theatra chorearum) and the courts of princes, not for churches (Theses 17-18). And any ‘church music with a measured beat’ is absolutely proscribed ‘as the most effective obstacle to devotions’ (Thesis 16).”
Leaver sums up: “Since Karlstadt has dismissed all forms of church music then known – Gregorian chant in the Mass, the Psalm tones of the daily Office, polyphony and the use of instruments – the only model he is left with is the vernacular strophic religious folk song.”
Which, Leaver argues, is exactly what Luther and others used as the basis for Reformation hymnody.