The people in Philistia knew something of Israel’s deliverance and exodus from Egypt (see 1 Samuel 4:8). They knew that the Lord is powerful and that he sent many plagues upon Egypt before the Israelites were eventually allowed to go. In light of this knowledge, the priests and diviners warned the Philistine leaders not to harden their hearts by keeping the ark and pretending as if the Lord had no hand in the plagues which they had experienced (see Exodus 4:21; Exodus 8:19, Exodus 8:32). They did not want the same destruction to come on Philistia as it had on Egypt.1
6 Why should you harden your hearts as the Egyptians and Pharaoh hardened their hearts? After he had dealt severely with them, did they not send the people away, and they departed?