They said, "If you send away the ark of the God of Israel, don't send it empty; but by all means return him a trespass-offering: then you shall be healed, and it shall be known to you why his hand is not removed from you."
Yahweh had reduced the fertility of the crops of the Philistines as well as afflicting the people and their gods (1 Samuel 6:5). The Philistines remembered that this is what Yahweh had done to the Egyptians earlier (1 Samuel 6:6). The priests counseled the people not to harden their hearts as Pharaoh had done. Hardening the heart only brings divine retribution (cf. Joshua 7:19).