Behold; if it goes up by the way of its own border to Beth-shemesh, then he has done us this great evil: but if not, then we shall know that it is not his hand that struck us; it was a chance that happened to us."
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).