We know that Jesus and his disciples often prayed the psalms and sang spiritual songs. Christians sing because they must. As there is no free will in matters of faith there is likewise no free will in song. Music is a gift from God in which he graciously sparks our hearts to sing out to God and to one another. Through hymnody we praise his work and comfort his saints.
Jesus was no stoic. He prayed, cried, laughed, and sang. As we have been brought through his living waters of baptism we arise and sing a new song that never ends. This song of the blessed Gospel is not only sung in the heavenly expanse but in the grime and misery of this world. In this way singing is of our prayers, tears, and joy - as our dear Lord himself. Because the Father sent the Son to be born of a woman in this world to ease our pain, he so sends us to be of good cheer to one another. To build one another up in love by song and prayer. Christ was not called out of this world, with his death, ressurection, and ascension but wholly into it. Flesh, blood, and living sacrifice to cover the ends of the earth. In this way his children who live by his spiritual milk are called wholly into this world as well as the heavens. Lutherans have sung during the plague, on the gallows, during wars and turmoil, bombing raids, concentration camps, and unspeakable horrors. As the billows rage and the world quakes the Lord has always led his flock to green meadows to drink at his still waters.
As there is no free will for the Christian to sing there is likewise no free will of the Father to withhold mercy. So long as the creation was helpless and needy he must hear their plea and song. So long is there the poor, the widow, and the fatherless God has ordained from the beginning that His Word will fight for them and always defend his flock - from the bitter pangs of death and defeat. For this reason he fights with a flaming sword and raises up the tree of life that all blessing may be freely given. For the promise is not conditional upon the will of man but only upon the unconditional will of God. The promise was to Abraham and to His Seed, which is Christ (Gal. 3:16). God's convenant - his redeeming act only he can promise. And only he can carry out. God's salvation is only a matter within himself, within a Son, whom he sent.
The Christian best sings when he sees that he can no longer wrestle for God's promise, and that it is freely given. When the Reformation began two young friars, Heinrich Voe and Johann Esch died for singing priase to this Gospel truth. They were burned at the market place in Brussels on July 1, 1523. Luther wrote a song in honor of their confession and bold witness to Christ - the Ballad of the two Brussels Martyrs