The next two Mishnayot (Mishnahs) will talk about a se'ah-for-a-se'ah deal that people made: one person lends another a certain amount of produce. For example, a se'ah is a measurement of produce. He does this only on the condition that the person who borrowed from him will give him back the same amount of produce. In general, this type of loan would not be permitted, as we'll elaborate on in the next Mishnah. The reason is that if he lends him a se'ah's worth of an item at one price, and by the time repayment is due the se'ah is worth much more, then when the borrower pays back that se'ah, he is basically paying interest because its value went up. So he wouldn't be able to give him the full se'ah; he'd have to give him less in order to avoid the interest. But this is generally prohibited because we don't want the borrower to give back a se'ah that would be worth more. Here, though, we'll start by talking about a situation where it is permitted.
The Mishnah says a person is allowed to lend his own sharecroppers. A sharecropper is somebody who farms on somebody else's field and gives the landowner a piece of the action—a piece of the crop that he eventually grows. The landowner is allowed to lend his sharecropper wheat for wheat. He's allowed to give him a certain amount of wheat kernels and later expect the same amount to be given back to him, because the kernels that he gives the sharecropper are going to be used for planting. The kernels here are not viewed as a loan, but as part of the agreement between the landowner and the sharecropper. The equity in the profits is split between them, as they had agreed, but the sharecropper is obligated to compensate the landowner for all the kernels he gave him. Generally, it's the sharecropper's obligation to plant those kernels. So here we're saying that he gave them to him, and it's not considered to be interest. It's not considered a problem to trade one measurement for another later, because it's part of their business agreement.
But he's not allowed to lend him wheat if the wheat is going to be used for eating, because that's considered to be a real loan, like a regular case of a se'ah for a se'ah. And if the price of the wheat goes up, initially, the sharecropper is obligated to give him back the exact measurement that he received. He would be giving him back more than he borrowed in value.
Now the Mishnah is going to say why they thought it necessary to tell us this halakha (Jewish law): Rabban Gamliel was accustomed to generally lending sharecroppers wheat for wheat. Because his sharecroppers wanted to plant, he gave it to them at a high price, and then the wheat became much cheaper. Or he gave them these wheat kernels at a low price, and then the wheat became more expensive. When he took the wheat back from them, he would always take it at the cheaper price. He would always get the raw end of the deal, the worst end of the deal, because he wanted to be very careful that it didn't look like he was taking interest. So if he gave it to them at a very low price and then the price went up, he wouldn't take the higher amount he was technically entitled to, because this is a sharecropper case. He could take it back; it's part of the business agreement, and we're not nervous about interest. Even so, Rabban Gamliel would take the lower amount, not the higher amount. He did not do this because he thought it was the law or because he felt obligated to; he did it only because he wanted to be strict with himself. The halakha is that when you're lending a sharecropper a se'ah for a se'ah to be used for planting, you're allowed to take back the full se'ah regardless of the price. It's not a problem. Rabban Gamliel, though, wanted to be strict with himself and didn't want it to appear that he was taking any interest, so he always took the lower amount to avoid collecting interest.