Charles Ellicott Commentary 1 Samuel 28:2

"And David said to Achish, Therefore thou shalt know what thy servant will do. And Achish said to David, Therefore will I make thee keeper of my head for ever." — 1 Samuel 28:2 (ASV)

And David said to Achish. —Sorely perplexed, David temporizes. He dares not refuse; and yet, the idea of commanding a Philistine division in a war with Israel was to him a terrible alternative.

And Achish said to David, Therefore I will make you keeper of my head forever. —The King of Gath, like so many others with whom the winning son of Jesse came in contact in his career, seems to have been completely won by his lovable, generous character, and would not see any ambiguity in David’s reply, but at once offers him in the coming campaign a most distinguished appointment in the army of Gath—the command of the bodyguard: for this is what Ewald understands the offer of King Achish to signify.

But, as we shall see, the blind confidence of the king was not fully shared by the Philistine chieftains; jealousy of the distinguished stranger captain opened their eyes to David’s real feelings (See 1 Samuel 29:3; 1 Samuel 29:11).

It is also quite conceivable that whispers concerning David's expeditions during the past year were current in some Philistine quarters. The king's eyes, these more far-seeing nobles thought, were blinded by his partiality for his military vassal (See Note on 1 Samuel 29:3).