That it is good and God pleasing to sing hymns is, I think, known to every Christian, for everyone is aware not only of the example of the prophets and kings in the Old Testament who praised God with song and sound, with poetry and psaltery, but also of the common and ancient custom of the Christian church to sing Psalms. St. Paul himself instituted this in I Corinthians 14 and exhorted the Colossians to sing spiritual songs and Psalms heartily unto the Lord so that God's Word and Christian teaching might be instilled and implanted in many ways.
Therefore I, too, in order to make a start and to give an incentive to those who can do better, have with the help of others compiled several hymns, so that the holy gospel which now by the grace of God has arisen anew may be noised and spread abroad.
Like Moses in his song [Exodus 15], we may now boast that Christ is our praise and song and say with St. Paul, I Corinthians 2, that we should know nothing to sing or say, save Jesus Christ our Savior.
And these songs were arranged in four parts to give the young–who should at any rate be trained in music and other fine arts–something to wean them away from love ballads and carnal songs and to teach them something of value in their place, thus combining the good with the pleasing, as is proper for youth. Nor am I of the opinion that the gospel should destroy and blight all the arts, as some of the super-religious claim. But I would like to see all the arts, especially music, used in the service of Him who gave and made them. I therefore pray that every pious Christian would be pleased with this and lend his help if God has given him like or greater gifts. As it is, the world is too lax and indifferent about teaching and training the young for us to abet this trent. God grant us his grace. Amen.
Via Luther's Works Vol. 53, pp. 315-16.