Jamieson, Fausset and Brown on 1 Samuel 29:4

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 (1Sa 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.