If the reasons Achish had to trust David were stronger than the reasons which the princes offered why they should distrust him (as I do not see that, in policy, they were, for the princes were certainly in the right), yet Achish was but one of five, though the chief, and the only one that had the title of king; accordingly, in a council of war held on this occasion, he was over-voted, and obliged to dismiss David, though he was extremely fond of him. Kings cannot always do as they would, nor have such as they would about them.
I. The discharge Achish gives him is very honourable, and not a final discharge, but only from the present service. 1. He signifies the great pleasure and satisfaction he had taken in him and in his conversation: Thou art good in my sight as an angel of God, Sa1 29:9. Wise and good men will gain respect, wherever they go, from all that know how to make a right estimate of persons and things, though of different professions in religion. What Achish says of David, God, by the prophet, says of the house of David (Zac 12:8), that it shall be as the angel of the Lord. But the former is a court-compliment; the latter is a divine promise. 2. He gives him a testimonial of his good behaviour, Sa1 29:6. It is very full and in obliging terms: "Thou hast been upright, and thy whole conduct has been good in my sight, and I have not found evil in thee." Saul would not have given him such a testimonial, though he had done far more service to him than Achish. God's people should behave themselves always so inoffensively as if possible to get the good word of all they have dealings with; and it is a debt we owe to those who have acquitted themselves well to give them the praise of it. 3. He lays all the blame of his dismission upon the princes, who would by no means suffer him to continue in the camp. "The king loves thee entirely, and would venture his life in thy hand; but the lords favour thee not, and we must not disoblige them, nor can we oppose them; therefore return and go in peace." He had better part with his favourite than occasion a disgust among his generals and a mutiny in his army. Achish intimates a reason why they were uneasy. It was not so much for David's own sake as for the sake of his soldiers that attended him, whom he calls his master's servants (namely, Saul's), Sa1 29:10. They could trust him, but not them. (4.) He orders him to be gone early, as soon as it was light (Sa1 29:10), to prevent their further resentments, and the jealousies they would have been apt to conceive if he had lingered.
II. His reception of this discourse is very complimental; but, I fear, not without some degree of dissimulation. "What?" says David, "must I leave my lord the king, whom I am bound by office to protect, just now when he is going to expose himself in the field? Why may not I go and fight against the enemies of my lord the king?" Sa1 29:8. He seemed anxious to serve him when he was at this juncture really anxious to leave him, but he was not willing that Achish should know that he was. No one knows how strong the temptation is to compliment and dissemble which those are in that attend great men, and how hard it is to avoid it.
III. God's providence ordered it wisely and graciously for him. For, besides that the snare was broken and he was delivered out of the dilemma to which he was first reduced, it proved a happy hastening of him to the relief of his own city, which sorely wanted him, though he did not know it. Thus the disgrace which the lords of the Philistines put upon him prove, in more ways than one, an advantage to him. The steps of a good man ore ordered by the Lord, and he delighteth in his way. What he does with us we know not now, but we shall know hereafter, and shall see it was all for good.

David said - what have I done? - Dr. Chandler and others may say what they will to make David act a consistent part in this business; but it is most evident, whatever his intentions might be as to the part he was to take in the approaching battle, he did intend to persuade Achish that he would fight against Israel; and affects to feel his reputation injured by not being permitted on this occasion to show his fidelity to the king of Gath.
It was in the order of God's gracious providence that the Philistine lords refused to let David go with them to this battle. Had he gone, he had his choice of two sins - First, If he had fought for the Philistines, he would have fought against God and his country. Secondly If he had in the battle gone over to the Israelites, he would have deceived and become a traitor to the hospitable Achish. God, therefore, so ordered it in his mercy that he was not permitted to go to a battle in which he was sure to be disgraced, whatever side he took, or with what success soever he might be crowned.

And David said unto Achish, what have I done?.... This question is anticipated by the speech of Achish, who had declared he had found no evil in him; but David must say something to put on an appearance of concern for being dismissed, when he was heartily glad of it:

and what hast thou found in thy servant, so long as I have been with thee unto this day, that I may not go fight against the enemies of my lord the king? which cannot be excused of great dissimulation, since nothing was more foreign from his heart, and against his will, than fighting against the Israelites, and which he determined to avoid if possible; and glad at heart he was to be thus excused, and freed from the straits and difficulties he was involved in; but that the Philistines might have no cause of suspicion of him, and that he was warmly attached to their interest among whom he was still to continue, he put on these airs. Abarbinel is of opinion that the lords of the Philistines were only afraid of David, but not of his men, and therefore were not solicitous about their going, but his, which gave David a concern; and since he was particularly singled out, he desired to know what special evil had been found in him; but when he understood, by the following answer of Achish, that his servants were to go with him, he was content, and said no more; but the princes asked, "what do these Hebrews here?" Sa1 29:3.

the princes of the Philistines were wroth with him--It must be considered a happy circumstance in the overruling providence of God to rescue David out of the dangerous dilemma in which he was now placed. But David is not free from censure in his professions to Achish (Sa1 29:8), to do what he probably had not the smallest purpose of doing--of fighting with Achish against his enemies. It is just an instance of the unhappy consequences into which a false step--a departure from the straight course of duty--will betray everyone who commits it.