Of all the idols in Egypt, only one survived the plagues: Ba'al Tzefon. The Mekhilta explains that God deliberately left this single idol standing — and then commanded Israel to camp right in front of it.
The strategy was a divine trap. By sparing Ba'al Tzefon while destroying every other Egyptian deity, God created the illusion that this particular idol had power. The Egyptians would look at the devastation of their pantheon and conclude that Ba'al Tzefon alone had the strength to save itself.
Then God told Israel: "Over against it shall you encamp by the sea." Camp directly in front of this last remaining idol. Make it look like you are trapped between the idol and the water.
The Mekhilta cites (Job 12:23): "He deceives the nations to destroy them." God was engineering the Egyptians' final delusion. Pharaoh and his army would see Israel hemmed in before Ba'al Tzefon and believe their god had cornered the fleeing slaves. This false confidence would drive them to pursue Israel into the split sea — and to their destruction.
The last idol standing was not a sign of strength. It was bait. God left it intact precisely so it could lure Egypt to its doom.