And it came to pass, when the evil spirit from God was upon Saul, that David took a harp, and played with his hand: so Saul was refreshed, and was well, and the evil spirit departed from him.
Read Chapter 16
Augustine of Hippo
AD 430
You, a man of the church, ought to be better instructed by the music of the church than by Pythagoras. Think what David’s lyre did for Saul, who was harassed by an evil spirit but recovered from this disturbance when the holy man played his lyre; beware of thinking the concupiscence of the flesh is a good merely because it is sometimes checked by musical sounds. - "Against Julian 5.5.23"
The discipline of music incorporates great power and knowledge which brings delight; teachers of secular literature, through the generosity of God who grants all that is useful, have made it possible through theoretical texts to ascertain what was earlier regarded as hidden from view in the nature of the world. The first division of this discipline, then, is into harmonics, rhythmics and metrics. The second division, that of musical instruments, is between percussion, strings and wind. The third division is into six harmonies, the fourth into fifteen tones. In this way the virtue of this most beautiful discipline is unfolded by such distinctions drawn by people of old. We read in secular works that many miracles were brought forth by these measures. But we need say nothing of this fabulous material; we read that by means of David’s tuneful harp the demon was expelled from Saul. The divine reading attests that the walls of Jericho at once collapsed at the din of trumpets. So there is no...
Departed from him. Chased away by David's devotion. (Challoner)
"The melody of David's harp, as some of the Fathers remark, represents that sweet and engaging demeanour, which should distinguish the peaceful ministers of the gospel. Whether they strive to allay the rage, or dispel the fears of a troubled mind. "(Reeves)
Nothing can equal the divine harmony of those sublime truths which are contained in the Psalms of David, and nothing can so powerfully contribute to drive away the spirit of pride from our hearts, and awaken them to the voice of heaven. (St. Augustine)
Some of these truths might make some passing impression even on the mind of Saul; and the devil could not bear to hear the praises of God. (Haydock)
Indeed, we should not disregard the fact that whenever the evil spirit possessed Saul, David took his harp and soothed his madness. What is symbolized by Saul but the pride of the mighty and what by David but the lowly life of the saints? As often, therefore, as Saul was possessed by the unclean spirit, his madness was soothed by David’s singing. So, too, whenever the disposition of people in power is turned to raving anger by pride, it is proper that we should recall them to a healthy frame of mind by gentle words, sweet tones of the harp, as it were. - "Pastoral Care 3.2"
Once when he came to Saul, who was frenzied and out of his right mind, he healed him by soothing his passions with song, so that Saul’s understanding returned to him again in accordance with nature. The goal, then, of the symbolism of the singing is clear from these words. It recommends that we achieve the subjugation of those passions which arise in us in various ways from the circumstances of life. - "On the Inscriptions of the Psalms 1.3.24"
After this, you will find plenty of men and women, filled with a divine spirit, who sang of the mysteries of God. Among these was David. As a boy, he was given a special call to this office, and by God’s grace he became the prince of singers and left us a treasury of song. He was still a boy when his sweet, strong song with his harp subdued the evil spirit working in Saul. Not that there was any kind of power in the harp, but, with its wooden frame and the strings stretched across, it was a symbol of the cross of Christ. It was the passion that was being sung, and it was this which subdued the spirit of the devil. - "Liturgical Singing 4"