From Luther’s preface to the 1545 Babst Hymnal: “God has cheered our hearts and minds through His dear Son, whom He gave for us to redeem us from sin, death, and the devil. He who believes this earnestly cannot be quiet about it. But he must gladly and willingly sing and speak about it so that others may come and hear it. And whoever does not want to sing and speak of it shows that he does not believe and that he does not belong under the new and joyful testament, but under the old, lazy, and tedious testament.” (Luther’s Works, Vol. 53, p. 333)
I got this from the “inVoice” newsletter that I get from the Seminary Chorus.