1Sam 16:14

“The devil has power that might be called his own, only over such as no longer belong to God, the heathen whom he considers once for all as a drop in a bucket, as dust on the threshing floor, as spittle in the mouth—and, as such, totally handed over to the devil as a quite useless possession.Otherwise, he may do nothing by his own right, against those who dwell in the house of God, because the cases that are noted in Scripture show us when—that is, for what reasons—he may touch them. The right to tempt a person is granted to the devil, either for the sake of a trial, as in the texts cited above, whether God or the devil initiates the plan, or for the purpose of the reprobation of a sinner, who is handed over to the devil as to an executioner. This was the case with Saul. "The spirit of the Lord departed from Saul, and an evil spirit from the Lord troubled and stifled him." Again, it may happen in order to humble a person, as Paul tells us that there was given him a thorn, a messenger of Satan, to buffet him, and even this sort of thing is not permitted for the humiliation of holy ones through torment of the flesh, unless it be done so that their power to resist may be perfected in weakness.”

“I will instruct you of that which is written, that the Spirit is not at every time found with those that receive it. For it is written about Saul, that the Holy Spirit, which he received when he was anointed, departed from him, because he grieved it, and God sent to him instead of it a vexing spirit. And whenever he was afflicted by the evil spirit, David used to play upon the harp, and the Holy Spirit, which David received when he was anointed, would come, and the evil spirit that was vexing Saul would flee from before it. So the Holy Spirit that David received was not found with him at every time. As long as he was playing the harp, then it used to come.”

“Therefore, when a person falls from the Spirit for any wickedness, if he repents after his fall, the grace remains irrevocably to the one who is willing; otherwise he who has fallen is no longer in God (because that Holy Spirit and Paraclete which is in God has deserted him), but this sinner shall be in him to whom he has subjected himself, as took place in Saul's instance; for the Spirit of God departed from him and an evil spirit was afflicting him.”

“Again, that you may be sure that God curbs the spirit of pride, recall how the good spirit of God departed from Saul and an evil spirit troubled him. Holy Writ says, "And an evil spirit of God troubled him," a spirit from God. Does God, then, have an evil spirit? Not at all. God had withdrawn so that afterwards an evil spirit might trouble Saul. In that sense, the spirit of God is called evil. Finally, holy David, knowing that God could take away the spirit of princes, entreats him, "And do not take your holy spirit from me."”

“But the Spirit of the Lord departed from Saul, etc. As the proclamation of Christ increased, the grace of the Spirit soon deserted the hearts of the faithless Jews, and incited them with impious fury to persecute his name; and this the Lord permitted by just judgment, so that the tested ones might be made manifest in the Church, and the wicked, by their deserving merits, might be plunged further into the depths of their own malice.”

“Behold, the evil spirit of God agitates you, etc. The apostles said to the Jews, desiring in all things to serve their salvation: See and recognize how evil the spirit is, which, because of your fault, has been sent by the Lord against your minds, to oppose the name of his only begotten Son, and has led you to conspire against him: yet now, having performed penitence for your errors, flee to the aid of the life-giving wood, where the innocent limbs of the same spotless Lamb of God and our Lord Jesus Christ are stretched out. For we seek, that is, we will obtain for you, faith by explaining it more fully if you wish, that man, very well known to us but still unknown to you, endowed with singular knowledge among men, who by the saving wood of his cross knows how to put to flight all the deadly weapons of the harmful adversary: so that whenever the devil begins to move you to envy against the grace of the Gospel, under the shadow of the law, the memory of the Lord's passion may be present, and may soon restrain your hearts from furious intention.”