In Parshas Behar the Am Yisroel is warned against deceiving one another in business transactions:
When you’re doing business with your fellow Jew, selling to him or buying from him, you should make sure not to vex him (Behar 25:14). It means: if you’re the seller, you shouldn't aggrieve him by cheating him, either in the price, or in the weight or quality of the merchandise. And if you’re the buyer, sometimes the seller might be deceived if you give him less money than it's worth and he doesn't know. So not only shouldn’t you overcharge, but you shouldn’t underpay either. Unfortunately it happens many times, people give checks that bounce. That’s not called underpaying – that’s robbery. A check has to be an honest check. But even if you pay the good check, it has to be paid properly. So whatever it is, whatever the details are, it’s the sin of ona’as mammon, of causing sorrow, vexation, to your fellow Jew in business matters. It’s a very serious crime.
But then, when the Torah comes to the end of this subject matter, there’s another possuk that seems to be repetitious. We’re warned the same thing a second time: And you should not aggrieve your fellow man. And the Gemara (Bava Metzia 58b) is bothered by that – what’s this repetition for? What is the second possuk telling us that the first possuk didn’t say?
And what the Gemara answers introduces us to an entirely new Torah commandment altogether, a new and important branch of Torah living: What is this second possuk coming to say? It’s talking about hurting a person with devarim, with words. The seeming repetition of these pessukim above actually is no repetition at all. It’s not speaking about preying on your fellow Jew’s money but about preying on his emotions – it’s a specific lav against speaking words that hurt a fellowman’s feelings. Just like there’s aggrieving a person with money, there’s also aggrieving him with words. It’s a Tosefta.
