Arachin, Chapter 9, Mishnah 2. This chapter deals with the sale and redemption of a sedeh achuzah, an ancestral field, and with the calculations that determine what the original owner must pay to get his land back before the yovel.
The preceding mishnah laid down the underlying rule. A purchaser of an ancestral field is really paying for a fixed run of crop years, since the land reverts to its family at yovel. The price is therefore broken up year by year: take the sum handed over and divide it by the count of years that stood between the sale and the yovel. Imagine a field that fetched a hundred dinar when ten years remained. Each year of use is thus valued at ten dinar. Should its former owner step forward once five years have elapsed, he pays fifty dinar, the worth of the five crop years the purchaser has not yet had.
When the buyer sells it to someone else
Our mishnah takes up a more complicated situation. The owner sold his field to a first buyer, and that buyer went ahead and sold it to a second buyer. Now the original owner wants his land back, but the person holding the field is someone he never dealt with. And what happens when the second sale was for a different price than the sale the owner himself made? On which figure is the redemption based?
The text opens: "mecharah larishon bemaneh", the original proprietor transferred his ancestral field to a first purchaser for a maneh, a sum of a hundred dinar. "Umachar harishon lasheni bematayim", that purchaser then passed the land along to a second one for two hundred. Such a resale is perfectly valid, since the first purchaser genuinely acquired rights in the land and was free to transfer them. In every event, however, the land goes back to the family that held it once yovel arrives, and until that point the family's power of redemption remains in force.
The ruling: "eino mechashev ela im harishon", he calculates only with the first buyer. The original owner works out his redemption price using the lower figure, the hundred dinar of the sale he himself made, and pays that amount to the second buyer, who is currently in possession, in order to take his field back. The two hundred dinar of a transaction he had no part in does not enter the calculation.
To follow it through: the field was sold for a hundred dinar with ten years left until the yovel, so each remaining year is valued at ten dinar. That is the rate the owner uses when he comes to redeem, and the later sale of two hundred dinar is simply irrelevant to him.
What is the basis for this? "Shene'emar, la'ish asher machar lo", the Torah directs the seller to compute the years of the sale together with the party who bought from him. That party is the one who took the land directly out of his hand, and no other. The verse thus anchors the calculation in the sum that came out of that opening transaction.
The reverse case
The mishnah then flips the numbers: "mecharah larishon bematayim umachar harishon lasheni bemaneh". This time the ancestral land passed from its proprietor to the initial purchaser for two hundred dinar, and that purchaser afterward handed it on to a second party for a mere maneh, a hundred dinar.
The verdict now runs the other way: "eino mechashev ela im ha'acharon", the reckoning is made with the final purchaser. Redemption is priced off the hundred dinar that the second party laid out, and not off the two hundred that changed hands in the opening sale. The proof text here is "la'ish asher betochah", the pasuk speaks of reckoning with the man who is inside the field, meaning whoever actually holds it at the moment, in our case the second purchaser. Since his was the cheaper acquisition, his figure is the one that governs.
The two verses together account for both directions. In one instance the calculation follows the deal the seller struck himself; in the other it follows the resale carried out later by his buyer. What decides between them is which of the two produces the lower annual rate, for the Torah arranged matters so that the man reclaiming his family's land is charged whichever figure works out to his advantage.
Restrictions on how the redemption money may be raised
The mishnah now sets out further conditions governing the redemption itself. Picture a man who owns two ancestral fields, one near and one distant. He has already sold the near one and wants it back, but he lacks the funds.
"Lo yimkor berachok veyigal bekarov", he may not raise the sum by disposing of the far field in order to recover the near one. "Vera veyigal beyafeh", nor may he unload a poor field to fund the recovery of a fine one. "Velo yilveh veyigal", taking a loan for this purpose is likewise ruled out; the funds have to be his own. "Velo yigal lachatza'in", and he cannot take the field back piecemeal. Lacking the full sum, he redeems nothing at all and waits until he has all of it.
Hekdesh is different
All of that applies to an ancestral field that a man sold to another person. But if he consecrated his ancestral field to the Temple treasury, the halachah changes: "uvahekdesh mutar bechulan", regarding hekdesh all of these are permitted. To redeem a field he dedicated to the Beit Hamikdash, he may sell another ancestral field, whether distant or superior, he may borrow money, and he may even redeem half the field.
Hence the closing line: "vezeh chomer bahedyot mibahekdesh", here the stringency falls on the ordinary transaction rather than on the consecrated one. Recovering land from a fellow Jew cannot be financed by such means, while recovering it from the Temple treasury may be financed by every one of them.