Why then do you harden your hearts, as the Egyptians and Pharaoh hardened their hearts? When he had worked wonderfully among them, didn't they let the people go, and they departed?
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).