He did that because their presence bothered him ~ 'cause, among other things, plagues of frogs were sent, the first-born were killed, people got boils, the river ran red, .......
Someday you just gotta' read the whole story!
The whole army of Egypt was sent out to bring back the Israelites, with the Pharaoh at their helm, and you term this as Pharaoh letting them go. Then you tell me, I need to read the whole account?
Wow.
The Pharaoh had seen ten plagues leveled on his people. His own son had been struck down during Passover night. Even then he hardened his heart and refused to let the Israelites remain free. This you refer to as him letting them go, as if it was a done deal.
If so, then how is it that he wound up on the bottom of the Red Sea being destroyed with the army of Egypt?
Later...