Psalms 144:9

"I will sing a new song unto You, O God" [Psalm 144:9]. "A new song" is of grace; "a new song" is of the new man; "a new song" is of the New Testament. But lest you should think that grace departs from the law, whereas rather by grace the law is fulfilled, "upon a psaltery of ten strings will I sing unto You." Upon the law of ten commandments: therein may I sing to You; therein may I rejoice to You; therein may "I sing to You a new song;" for, "Love is the fulfilling of the law." [Romans 13:10] But they who have not love may carry the psaltery, sing they cannot. Contradiction cannot make my psaltery to be silent.

O God, I will sing to you a new song. A new man, a new song. O God, I will sing to you a new song. 'Sing to the Lord a new song.' How beautifully he did not say, I sing, but, I will sing. In the future he made his promise; for in the present he knows there is a battle, not a song. An army never sings, except when it has conquered. Therefore since in the present I fight, I have no leisure to sing. When I shall have conquered, then I will sing. On the ten-stringed psaltery I will make music to you. Then I will stretch out both hands, and on such strings I will sing to you. My prayer is your psaltery.

As it is written, "O God, I will sing you a new song, on a harp of ten strings I will play to you," we take the harp of ten strings to be the Ten Commandments of the law. Now to sing and play is usually the occupation of lovers. The old person, you see, is in fear; the young is in love. In this way also we distinguish the two testaments or covenants, the old and the new, that the apostle says are allegorically represented by the sons of Abraham, one born of the slave woman, the other of the free; "which," he says, "are two covenants." Slavery, surely, goes with fear, freedom with love, seeing that the apostle says, "You have not received the spirit of slavery again in fear, but you have received the spirit of sonship by adoption, in which we cry out, Abba, Father." And John says, "There is no fear in charity, but perfect charity throws out fear." So it is charity that sings the new song.True, that slavish fear embodied in the old person can indeed have the harp of ten strings, because that law of the Ten Commandments was also given to the Jews according to the flesh, but it cannot sing to its accompaniment the new song. It is under the law and cannot fulfill the law. It carries the instrument but does not manage to play it; it is burdened, not embellished, with the harp. But any under grace, not under law, they are the ones who fulfill the law, because for them it is not a weight to shoulder but an honor to wear; it is not a rack for their fears but a frame for their love. Fired by the spirit of love, they are already singing the new song on the harp of ten strings.