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 those restless enemies of Israel.
Achish said to David, 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.