Mishnah 8 in Chapter 5 moves to the topic of a "se'ah for a se'ah" loan, which means lending measure for measure: A person lends his friend a measure of merchandise or commodity, and expects to receive that exact same measure back - he lends a gallon of wine and expects to get a gallon of wine back. The Sages forbade this, as the concern is that practically the borrower will lose out and be required to pay much more in terms of value: He borrowed wine worth one hundred shekels, and at the time of repayment the price of wine went up and he ends up returning a value of two hundred shekels. It turns out that there is a practical result of interest here.
Why this is not a Torah prohibition but rather rabbinic:
There is no fixed interest here - the borrower did not commit in advance to return more than he received.
The Torah follows what was established at the time of the loan, and at that time the wine was equal to the wine. Therefore, there is no Torah prohibition here, even though the matter is forbidden rabbinically.
The proper way to make a "se'ah for a se'ah" loan:
Our Mishnah will teach that even though this problem exists, the proper way for someone who is about to do this is to set the price in advance and link the loan to it: The lender gives the merchandise based on the accepted price at the time of the loan, and the borrower returns according to that value, and this condition is set from the outset. However, there are leniencies: Those same leniencies that apply in commercial transactions due to the rules of "he has it" and "the market price has emerged" apply equally to a "se'ah for a se'ah" loan, and in fact, for a "se'ah for a se'ah" loan there are even more leniencies. We will discuss these leniencies in this Mishnah and the following one.
The Mishnah: Lending seeds to a sharecropper:
The Mishnah establishes that a person may lend his sharecropper wheat in exchange for the same amount of wheat, provided that the purpose is for planting - to plant the fields; but he may not do so for the sharecropper to eat the wheat. Meaning, he cannot lend him a se'ah of wheat so that he can make bread from it for the winter, and in the summer, when the harvest season arrives, the sharecropper returns a se'ah of wheat to him - for this is the forbidden "se'ah for a se'ah" loan.
A tenant farmer and a sharecropper:
We learned above, a few Mishnahs ago, the law of the tenant farmer - the renting farmer. In both scenarios the situation is the same: One person has land, and his friend has no land but seeks to make a living and is willing to work. He closes a deal and says: "Let me sit on your land, I will work it and I will share some of the profits of my labor with you." There are two ways to make this agreement regarding the payment in crops - a fixed amount or a variable amount:
Tenancy: A fixed payment, like rent - "Let me work your land and I will pay you ten se'ahs a year." We have already discussed this previously.
Sharecropping: This is what our Mishnah discusses. The sharecropper works the land in exchange for a portion of the crop, and they agree to divide the yield of the field - a third to the landowner and two thirds to the sharecropper, or however they agree - and whatever comes out, comes out.
Our Mishnah says that if the sharecropper said: "So that we can get the most out of the field that I am working for you, I need enough seeds to plant it fully, and I have no seeds nor the money to buy them. Provide me therefore with seeds, and I will return them to you at the end of the season when I have the crop from the field" - this is the meaning of "Le'zera" - for planting, in the Mishnah: The sharecropper takes the seeds for planting the fields.
When the time for payment arrives, the sharecropper will not just return a third of the crop, or whatever they agreed upon in advance, but a third of the crop plus the se'ah of wheat kernels that he borrowed. Ostensibly, this looks like the repayment of the principal of a loan, and therefore like the rabbinically forbidden "se'ah for a se'ah". But the Mishnah teaches that there is no prohibition here, because we treat all of this as part of the business deal between them: The worker in the field is actually in a combination of tenancy and sharecropping, and the deal made between them is that he pays a third of the crop plus one se'ah of wheat, in exchange for the permission to work and live on the land and receiving seeds to plant the field. Because this is a business transaction, the matter is permitted and is not considered a loan at all.
The Stringency of Rabban Gamliel:
The Mishnah continues and teaches that although this is the baseline halachah, Rabban Gamliel, who was a Nasi, did not act this way and was strict with himself. He owned fields and had sharecroppers, and when he would "lend" to his sharecropper - meaning he would supply him with seeds for planting - he would always arrange the deal in a way that the sharecropper would benefit from it: if the grain became more expensive, to the sharecropper's detriment, he would take from him only its original monetary value, so the sharecropper ended up returning less grain; and if its value dropped, he would take only the amount of grain that was borrowed and no more. Either way, the borrower does not lose out. However, this is a stringency that Rabban Gamliel took upon himself, and it is not the baseline halachah.
This is the text of the Mishnah: "Shehayah Rabban Gamliel malveh et arisav chitin bechitin lezera" - he would say to them: I am giving you now a se'ah of wheat to plant the field, and you will return a se'ah to me later on. "Hukru vehuzelu, o huzelu vehukru, notel mehen kesha'ar hazol" - whether the price went up or down, when Rabban Gamliel came to collect the repayment for the seeds, he would take whichever was more beneficial for the borrower, who is the sharecropper. "Velo mipnei shehalachah ken" - this is not the baseline halachic requirement, but rather Rabban Gamliel wanted to be strict with himself, so as not to create even the impression of generating a profit that has a semblance of a Rabbinic prohibition of interest.
The halachah, of course, does not follow Rabban Gamliel but rather the Tanna Kamma: it is permissible to lend to a sharecropper, because we do not treat this as a loan at all, but rather as a business transaction.