What possessed Pharaoh to pursue the Jewish People, whom he had just (forced by Hashem) released from bondage? What was running through his mind when he made such an about-face? He had just suffered ten devastating plagues, with the death of the firstborn Egyptians striking very close to home. His people were demoralized, his country in ruin; yet, he was chasing the Jews. Did he require more proof of Hashem’s power? He arrived with his soldiers at the banks of the Red Sea and saw that the sea had miraculously split, and the Jews were crossing through on dry land. Did he think that the sea had been split for him? Did he not realize that to enter into the sea was suicidal? Pharaoh’s actions bespeak a man who has lost his mind.
Horav Chaim Kanievsky, Shlita, explains/rationalizes (if such a term is possible) Pharaoh’s actions, based upon a halachah found in the Yerushalmi (Bava Metzia 4:3). Onaah, overreaching, refers to the laws surrounding monetary deception, the act of wrongdoing another by selling him an article for more than its real worth. Chazal distinguish three levels of onaah: when the discrepancy amounts to one-sixth; less than one-sixth; more than one-sixth of the value. When the discrepancy overreaches by one-sixth – the transaction is valid, and he need not repay the difference. If the discrepancy amounts to more than one-sixth, the transaction is void. The injured party, however, may uphold the transaction if he so chooses. The Yerushalmi questions the last halachah, which voids the sale in the event that the discrepancy overreaches one-sixth. Why can the seller not repay the injured party the money and validate the sale? Rabbi Zeira says, “The buyer can say to the seller, ‘I am not comfortable having people say that you succeeded in cheating me. (I do not want people on the street conjecturing that I am a pushover, naïve in business – I could be sold anything for any price).’” In other words, it is not about the money. It is about one day the injured party screaming, “He ripped me off,” and the next day making a settlement with him. The buyer’s reputation is at stake.
Certainly, Pharaoh remembered the travail that he and his country had sustained the last few months, but he could not tolerate being cheated by the Jews. They went from home to home borrowing gold and silver utensils, and now they were leaving town with those utensils. The Egyptian People would not stand idly by as they were being ripped off by the Jews. He could not overlook this infraction, and he was willing to risk death to prevent it. His ego would not allow them to leave with his gold and silver.
Alternatively, I think we can add (along the same lines) “regarding the people,” the Torah underscores that Pharaoh could not tolerate this behavior on the part of the “people,” since their forebears had been their slaves, chattel to do with them whatever they pleased. Now, they were leaving the country as kings. This was just too much. Pharaoh would put an end to it – at all costs. He definitely paid!