Arachin, Chapter 7, Mishnah 3. The subject of this chapter is the field a man inherits from his family, his sdei achuzah, and the halachot that govern it once he consecrates it to hekdesh. The question our mishnah settles is this: when Yovel comes around, in whose hands does such a field end up?
Start with a contrast. When a man sells his ancestral field, Yovel restores it to him. When he consecrates it instead, Yovel likewise strips it from whoever happens to be holding it, yet the land does not automatically travel back to the family that once owned it. The Torah rules that if the original owner never bought his field back out of hekdesh, then once Yovel arrives the land becomes the property of the kohanim. The details of that halachah are what our mishnah lays out.
The Owner Redeems It Himself
"Hikdishah u'ge'alah": the owner consecrated his inherited land to hekdesh, and later, while Yovel was still off in the future, he paid and took it back himself. Concerning him the mishnah teaches "einah yotzah miyado bayovel", Yovel does not pull the land away from him. The kohanim have no claim on it. It remains where it is, because the man holding it is both the original owner and the one who redeemed it.
When His Son Redeems It
"Ge'alah b'no, yotzah l'aviv bayovel": the owner did not redeem, but his son paid hekdesh and took the land out. When Yovel arrives the field does not stay with the son, nor does it go to the kohanim: it goes to the father. An act of redemption performed by a son counts halachically as though the father had performed it himself.
What is the source? The pasuk speaks of an owner who does not redeem, after which the treasurer sells the consecrated land l'ish acheir, to another man. In that scenario the field reverts to hekdesh when Yovel comes, and the kohanim receive it. The phrase l'ish acheir points to a true stranger, a person standing outside the owner's own family circle. A son hardly fits that description, and so where the son was the redeemer, Yovel restores the land to the father.
From all of this the governing principle stands out clearly: consecrated ancestral land that reaches Yovel with no redemption ever having taken place becomes the portion of the kohanim.
An Outsider Redeems, and the Owner Buys It Back
The mishnah continues: "Ge'alah acheir", a stranger paid hekdesh and took the land, "o echad min hakrovim", or the redeemer was a member of the owner's family, "u'ge'alah miyado", and afterward the owner purchased the field back from whoever was holding it. Here too, "einah yotzah miyado bayovel": Yovel does not dislodge it from him. True, the land had passed through a second party's hands, but that is not the deciding factor. What decides is the situation at the moment Yovel arrives, and at that moment the field sits with the man who owned it to begin with. It therefore stays his afterward as well.
The reverse case follows from the same rule: if another person redeemed the dedicated field from the treasury and that field was still in the hands of this redeemer, who is not the original owner, when the Yovel came, the field reverts to the treasury and the kohanim divide it among themselves.
When the Redeemer Is a Kohen
The mishnah now turns to a kohen. Review the framework: land was consecrated to hekdesh, a stranger redeemed it and held it, and since the owner never took it back, Yovel returned the field to hekdesh, from where it was apportioned among the kohanim, meaning the mishmar, the watch on duty at that hour. Suppose now that the redeemer was himself a kohen belonging to that very mishmar, and Yovel found the field under his control.
"Ge'alah echad min hakohanim": no redemption was ever made by the owner, and it was a kohen who paid hekdesh and took the land, "harei hi tachat yado", so that Yovel arrives with the field under his hand. Such a kohen, the mishnah warns, "lo yomar", must not reason as follows: "Ho'il v'hi yotzah", since the field is headed out anyway, "al hakohanim bayovel", to the kohanim when Yovel comes, "v'harei hi tachat yadi", and I happen to be holding it right now, "harei hi sheli", let it simply belong to me.
"Ela yotzah", rather it does go out of his hand, "al kol echav hakohanim", to all his brother kohanim, the watch attending to the service at the time Yovel comes. The Torah assigned this land to that entire group. Consequently the kohen who was holding the field receives exactly what each of his colleagues receives, a single portion. His grip on the land gives him no advantage; it is split evenly with all of them.