1 Samuel 28:1

And it came to pass in those days, that the Philistines gathered their armies together for warfare, to fight with Israel. And Achish said unto David, Know thou assuredly, that thou shalt go out with me to battle, thou and thy men.

The Philistines gathered their armies together for warfare, to fight with Israel. The death of Samuel, the general dissatisfaction with Saul, and the absence of David, instigated the cupidity of these restless enemies of Israel, and they prepared to invade the kingdom.

Know thou assuredly, that thou shalt go out with me to battle. This was evidently to try him. Achish, however, seems to have thought he had gained the confidence of David, and had a claim on his services.