Matthew Henry on 1 Samuel 29:1-5
Here is, I. The great strait that David was in, which we may suppose he himself was aware of, though we read not of his asking advice from God, nor of any project of his own to get clear of it. The two armies of the Philistines and the Israelites were encamped and ready to engage, Sa1 29:1. Achish, who had been kind to David, had obliged him to come himself and bring the forces he had into his service. David came accordingly, and, upon a review of the army, was found with Achish, in the post assigned him in the rear, Sa1 29:2. Now, 1. If, when the armies engaged, he should retire, and quit his post, he would fall under the indelible reproach, not only of cowardice and treachery, but of base…
Read the whole note in the consoleJamieson-Fausset-Brown on 1 Samuel 29:4
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.
Adam Clarke on 1 Samuel 29:4
The princes of the Philistines were wroth - It is strange that they had not yet heard of David's destruction of a village of the Geshurites, Gezrites, and Amalekites, Sa1 27:8, Sa1 27:9. Had they heard of this, they would have seen much more cause for suspicion.
John Gill on 1 Samuel 29:5
Is not this David, of whom they sang one to another in dances,.... Long ago:
saying, Saul slew his thousands, and David his ten thousands; so that he is an old sworn enemy of ours; and the more valiant and victorious he has been, the less is he to be trusted, see 1 Samuel 18:7.
Keil & Delitzsch