Arachin, Chapter 7, Mishnah 2. This chapter is occupied with the laws of a sdeh achuzah, an ancestral field that has been consecrated to the Beit Hamikdash, and with the fixed rate at which such a field is redeemed: fifty shekalim for every beit se'ah of a full Yovel cycle. Our mishnah turns to the question of who does the redeeming. Is the original owner in a different position from anyone else who steps forward?
In one respect, no. The owner has no exclusive claim here; the field is open to whoever wishes to redeem it, and the same schedule of payment applies. But in one respect the owner is treated differently, and it costs him.
The Language of the Mishnah
The opening words are "echad hab'alim v'echad kol adam": the phrase places the man who once held the field and a complete stranger on identical footing. Each of them is entitled to redeem the sdeh achuzah, and each pays according to the same measure, fifty shekalim for every beit se'ah.
The mishnah then sharpens the issue with a question of its own: "Mah bein hab'alim l'vein kol ha'adam?" If the rate of redemption is one and the same for both, in what way does the former proprietor stand apart from everyone else?
The answer: "Ela shehab'alim notnin chomesh, v'chol adam eino noten chomesh." The owner pays an added chomesh, a fifth; anyone else pays no such addition.
How the Fifth Is Calculated
Take a case where the field is redeemed at the very start of the Yovel cycle, so that the full rate of fifty shekalim per beit se'ah applies. Someone other than the owner hands over fifty and the redemption is complete. The owner hands over fifty plus a chomesh.
Now, the chomesh here is not reckoned as a fifth of the base price, but as a fifth of the total sum the payer ends up laying out. The addition is therefore one of five equal parts of the final figure, which works out to a quarter of the original fifty.
In practice: the owner adds twelve and a half shekalim. That addition, multiplied by five, gives sixty two and a half, which is precisely what he pays in the end. Twelve and a half is exactly one fifth of that total. So the owner parts with sixty two and a half shekalim, while any other person redeems the same field for fifty.
Why the Difference?
There is no market logic behind this; the field is worth what it is worth regardless of who is standing at the counter. The added fifth is a gezeirat hakatuv, a decree of the verse. The pesukim state that when the one who consecrated the field comes to redeem it himself, he adds a fifth to the valuation. Hence the twelve and a half shekalim layered on top of the fifty that everyone else pays.