And David said to Achish, surely thou shalt know what
servant can do
By which he would have Achish understand, and so he did, that he would exert himself in favour of the Philistines, and against Israel, and do great and brave things, of which Achish would be, made sensible, through his heroic courage and valour; though he meant rather what he could and should do for Israel against the Philistines, if he had an opportunity: but it seems best of all to consider David as quite undetermined, and at a loss what to do, hoping that God in his providence would extricate him out of this difficulty, and direct him what he should do, which then Achish would know; and accordingly he was delivered out of it:
and Achish said to David:
putting confidence in him on account of his answer, and believing he was hearty in engaging in the war with the Philistines against Israel:
therefore will I make thee keeper of mine head for
the captain of his bodyguard, which post he should hold for life; or he proposed to put him into this post, that he might be with him, near his person, and under his eye, that he might observe how he behaved himself; which may show some suspicion of him.