And so it was, whenever the spirit from God was upon Saul, that David would take a harp and play it with his hand. Then Saul would become refreshed and well, and the distressing spirit would depart from him.
— First Samuel 16:23
Immediately after he was anointed, David entered a long period of testing. He was not instantly recognized as the new king. Saul remained as king. However, the Spirit of the Lord departed from Saul, and a distressing spirit troubled him. Saul’s servants suggested that a skillful harp player could make Saul well at such times, so David was called in to play (1 Sam. 16:14–23).
David, knowing that he was anointed to be king, served Saul and did what he could for him. He played his harp to soothe Saul and also became his armor bearer. Someone in David’s position might have been tempted to allow the evil spirit to do its work of tormenting Saul. Though David was anointed to be king after Saul, he did nothing to hasten Saul’s downfall; instead, he served and honored him.
Adapted from David: After God’s Heart, pages 47-48.