David plays the harp for King Saul (I Samuel 16:23, date: 1905-1916) - Public Domain Bible Painting

According to the Bible, David played the harp for King Saul when an "evil spirit from the Lord" was upon him^{[1][2][3][4][5]}. The music was thought to have a therapeutic effect and would help Saul relax and feel better, causing the evil spirit to depart from him^[1][4]. This is described in 1 Samuel 16:23 which states: "And it came to pass, when the evil spirit from God was upon Saul, that David took an harp, and played with his hand: so Saul was refreshed, and was well, and the evil spirit departed from him"^[3].