Our Gemara on Amud Aleph discusses a particular curse that befalls one who reneges on a transaction after money was exchanged. We have learned that exchange of money alone does not accomplish acquisition without the physical object being moved or lifted. Therefore, even though technically no transfer was completed yet, and legally he can stop the process, it is an ethical violation by going back on his word after the giving and accepting of payment. If he reneges, it is his right, but the following curse applies:

He Who exacted payment from the people of the generation of the flood, and from the people of the generation of the Tower of Bavel, and from the inhabitants of Sodom and Gomorrah, and from the Egyptians in the Red Sea, will in the future exact payment from whoever does not stand by his word.

It is notable that this curse only applies when a significant action and commitment was demonstrated by the payment. If they merely verbally agreed without payment, and it is still dishonorable and improper to go back on one’s word, it does not incur a curse (Shulchan Aruch CM 204:7). Therefore, we have a twofold standard. One may not renege on a verbal agreement, but if he does, there is no curse. But if money was exchanged, even though a full legal transfer was not effectuated, to renege will generate a curse.

Various commentaries offer explanations for invoking the four historical sinners in the curse, with the basic idea being that all of them were notorious for being deceitful. Sodom and the generation of the flood are obvious examples, but Pharaoh was also deceitful in that he agreed to let the Jews go, and then changed his mind many times.The exception being the generation of the Tower of Bavel whose sin does not seem to be deceit. On the contrary, the Midrash says that unlike the generation of the flood, the builders of the Tower of Bavel merited to be spared from a divine death decree because they got along well (Avos DeRabbi Nasan 12:7.)  Meiri in our Gemara notes this and says they were included only because they were an ancient group of sinners that were part of the overall timeline of degenerate societies. I would suggest that the generation of the Tower acted deceitfully with God, as they violated their side of the Rainbow covenant. Instead of submitting to God’s moral authority, they tried to storm Heaven and prevent a flood by force, (so implies Sanhedrin 109a.)

Another linguistic feature of this curse is that it refers to the “Egyptians in the Red Sea.” Why the Red Sea? Pharaoh and the Egyptians surely suffered enough during the plagues for this to be a robust curse. We might answer, as midrashically interpreted in the Pesach Haggadah, the Egyptians suffered 25 times more plagues at the Sea than in Egypt, and so the curse refers to the last and the worst punishment. I am not satisfied with this answer as the curse could have more briefly stated the “Egyptians”, without adding the clause, “at the sea”, and this would include all the punishments. I therefore believe the answer is as follows and reflects the two-tiered Halacha, of going back on one’s word without money exchange and/or with the addition of payment.

It’s true that Pharaoh went back on his word many times, but those were mere verbal agreements. However, when he finally let them leave, this was now a physical act, which demonstrated more commitment and obligation, just as a payment does. Pharaoh’s backtracking now warranted a curse. We reference the Egyptians at the sea in this curse, because it was particularly deceitful that after letting the Jews leave, and action was taken to demonstrate agreement, the Egyptians then reneged and chased after the Jews at the Red Sea.

Why does one dishonesty result in a curse while the other does not? Of course we can say it is a matter of severity. But I think it is deeper. Not standing by one’s word, though is to some extent interpersonal, it is more of an internal distortion than a kind of cheating. In that case, the rabbis were less interested in enforcement and maintaining the social contract versus disciplining the person for his own moral development. However, if money was exchanged, though technically not a theft since the object was not yet acquired, it is still close enough to interpersonal treachery that it requires enforcement and punishment, and hence the necessity for a curse.