The Spirit of the Lord departed from Saul - He was thrown into such a state of mind by the judgments of God, as to be deprived of any regal qualities which he before possessed. God seems to have taken what gifts he had, and given them to David; and then the evil spirit came upon Saul; for what God fills not, the devil will.
An evil spirit from the Lord - The evil spirit was either immediately sent from the Lord, or permitted to come. Whether this was a diabolic possession, or a mere mental malady, the learned are not agreed; it seems to have partaken of both. That Saul had fallen into a deep melancholy, there is little doubt; that the devil might work more effectually on such a state of mind, there can be but little question. There is an old proverb, Satan delights to fish in troubled waters; and Saul's situation of mind gave him many advantages.
The theory of Dr. Scheuchzer, in his Physica Sacra, on the malady of Saul, is allowed to be very ingenious. It is in substance as follows: Health consists in a moderate tension of the fibres, which permits all the fluids to have an entire freedom of circulation, and to the spirits, that of diffusing themselves through all the limbs; on the contrary, disease consists in tensions of the fibres morbidly weak or morbidly strong. This latter seems to have been the case of Saul; and as the undulations of the air which convey sound communicate themselves to and through the most solid bodies, it is easy to suppose that by the modulations of music all the fibres of his body, which were under the influence of the morbidly increased tension, might be so relaxed as to be brought back into their natural state, and thus permit the re-establishment of a free and gentle circulation of the fluids, and consequently of the animal spirits, and thus induce calmness and tranquillity of mind. I believe this theory to be correct, and I should find no difficulty to amplify and to illustrate the subject. Even a skillful playing upon the harp was one means to bring a disordered state of the nervous and fibrous system into a capacity of affording such uninterrupted tranquillity to the mind as to render it capable of receiving the prophetic influence; see the case of Elisha, 2-Kings 3:14, 2-Kings 3:15. It has been said: -
"Music hath charms to sooth the savage breast."
This has been literally proved: a musician was brought to play on his instrument while they were feeding a savage lion in the tower of London; the beast immediately left his food, came towards the grating of his den, and began to move in such a way as to show himself affected by the music. The musician ceased, and the lion returned to his food; he recommenced, and the lion left off his prey, and was so affected as to seem by his motions to dance with delight. This was repeatedly tried, and the effects were still the same.

But the Spirit of the LORD departed from Saul, and an (e) evil spirit from the LORD troubled him.
(e) The wicked spirits are at God's commandment to execute his will against the wicked.

But the Spirit of the Lord departed from Saul,.... As a spirit of prophecy as at first, as a spirit of wisdom and prudence in civil government, and as a spirit of fortitude and courage, as the Targum:
and an evil spirit from the Lord troubled him; the reverse of the former, which by the permission of God, and as a punishment to him for his sins, came upon him; he seemed to be a demoniac, as Josephus represents (i) him, as if possessed with the devil; by whom he was almost suffocated and strangled, as well as was distracted in his counsels, and became weak and foolish; lost all courage and greatness of mind, was timorous and fearful, and alarmed by everything, and was full of envy, suspicion, rage, and despair.
(i) Antiqu. l. 6. c. 8. sect. 2.

Saul is made a terror to himself. The Spirit of the Lord departed from him. If God and his grace do not rule us, sin and Satan will have possession of us. The devil, by the Divine permission, troubled and terrified Saul, by the corrupt humours of his body, and passions of his mind. He grew fretful, peevish, and discontented, and at times a madman. It is a pity that music, which may be serviceable to the good temper of the mind, should ever be abused, to support vanity and luxury, and made an occasion of drawing the heart from God and serious things. That is driving away the good Spirit, not the evil spirit. Music, diversions, company, or business, have for a time often been employed to quiet the wounded conscience; but nothing can effect a real cure but the blood of Christ, applied in faith, and the sanctifying Spirit sealing the pardon, by his holy comforts. All other plans to dispel religious melancholy are sure to add to distress, either in this world or the next.

The Spirit of the Lord departed from Saul, and an evil spirit from the Lord troubled him--His own gloomy reflections, the consciousness that he had not acted up to the character of an Israelitish king, the loss of his throne, and the extinction of his royal house, made him jealous, irritable, vindictive, and subject to fits of morbid melancholy.

David's Introduction to the Court of Saul. - 1-Samuel 16:14. With the rejection of Saul on the part of God, the Spirit of Jehovah had departed from him, and an evil spirit from Jehovah had come upon him, who filled him with fear and anguish. The "evil spirit from Jehovah" which came into Saul in the place of the Spirit of Jehovah, was not merely an inward feeling of depression at the rejection announced to him, which grew into melancholy, and occasionally broke out in passing fits of insanity, but a higher evil power, which took possession of him, and not only deprived him of his peace of mind, but stirred up the feelings, ideas, imagination, and thoughts of his soul to such an extent that at times it drove him even into madness. This demon is called "an evil spirit (coming) from Jehovah," because Jehovah had sent it as a punishment, or "an evil spirit of God" (Elohim: 1-Samuel 16:15), or briefly "a spirit of God" (Elohim), or "the evil spirit" (1-Samuel 16:23, compare 1-Samuel 18:10), as being a supernatural, spiritual, evil power; but never "the Spirit of Jehovah," because this is the Spirit proceeding from the holy God, which works upon men as the spirit of strength, wisdom, and knowledge, and generates and fosters the spiritual or divine life. The expression רעה יהוה רוּח (1-Samuel 19:9) is an abbreviated form for יהוה מאת רעה רוּח, and is to be interpreted according.

Departed - God took away that prudence, and courage, and alacrity, and other gifts wherewith be had qualified him for his public employment. From the Lord - That is, by God's permission, who delivered him up to be buffeted of Satan. Troubled - Stirred up in him unruly and tormenting passions; as envy, rage, fear, or despair. He grew fretful, and peevish, and discontented, timorous and suspicious, frequently starting and trembling.