And David said to Achis: But what have I done, and what hast thou found in me thy servant, from the day that I have been in thy sight until this day, that I may not go and fight against the enemies of my lord the king?

And David saith unto Achish, 'But what have I done? and what hast thou found in thy servant from the day that I have been before thee till this day, that I go not in and have fought against the enemies of my lord the king?'

And David said to Achish, But what have I done? what have you seen in your servant while I have been with you till this day, that I may not go and take up arms against those who are now making war on my lord the king?

And David said to Achish, "But what have I done, or what have you found in me, your servant, from the day that I was in your sight to this day, so that I may not go out and fight against the enemies of my lord, the king?"

See 1-Samuel 29:10 note.

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, But what have I done? and what hast thou found in thy servant so long as I have been with thee unto this day, that I may (e) not go fight against the enemies of my lord the king?
(e) This deception cannot be excused, for it grieved him to go against the people of God.

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?" 1-Samuel 29:3.

David said &c. - This was deep dissimulation and flattery, no way to be justified. None knows, how strong a temptation they are in to compliment and dissemble, which they are in who attend great men.