10 And it happened on the next day that the distressing spirit from God came upon Saul, and he prophesied inside the house. So David played music with his hand, as at other times; but there was a spear in Saul's hand.

Matthew Henry's Commentary on 1 Samuel 18:10

Commentary on 1 Samuel 18:6-11

(Read 1 Samuel 18:6-11)

David's troubles not only immediately follow his triumphs, but arise from them; such is the vanity of that which seems greatest in this world. It is a sign that the Spirit of God is departed from men, if, like Saul, they are peevish, envious, suspicious, and ill-natured. Compare David, with his harp in his hand, aiming to serve Saul, and Saul, with his javelin in his hand, aiming to slay David; and observe the sweetness and usefulness of God's persecuted people, and the barbarity of their persecutors. But David's safety must be ascribed to God's providence.