1 Samuel 28:1

And it came to pass in those days
That David was in the country of the Philistines:

that the Philistines gathered their armies together:
out of their five principalities or lordships:

for warfare to fight with Israel;
with whom they were continually at war, and though sometimes there was a cessation of arms, yet never any settled peace; and the Philistines took every opportunity and advantage against them, as they now did; when David was among them, and so had nothing to fear from him, but rather expected his assistance; and Samuel was dead, and Saul in a frenzy:

and Achish said unto David:
who seems to have been at the head of the combined armies of the Philistines:

know thou assuredly that thou shall go with me to battle, thou and thy
men;
against Israel; which was a trying thing to David, and whereby he was like to be drawn into a dilemma; either to fight against his country, which he could not do conscientiously; or be guilty of ingratitude to Achish, and incur his displeasure, and be liable to be turned out of his country, or treated in a worse manner, even he and his men, to be seized on and cut to pieces by the forces of the Philistines, should he refuse.