The mishnah before us deals with the question of how long the wife of a kohen may continue eating Terumah once she has appointed an agent to handle her get. Three cases are taught here, and each one fixes a different moment at which the marriage comes to an end.
"Havei li giti" - she eats until the get reaches her hand:
A woman who tells an agent "Havei li giti" - "Bring me my get" - has made him an agent for delivery. In this case the wife of a kohen continues eating Terumah until the get actually reaches her hand, since until that moment she is considered fully married. This rests on the principle explained at the end of the previous mishnah: the language of agency is not the language of one's own hand - the agent is not treated as the woman's hand, and the get does not take effect until it literally reaches her hand.
"Hiskabel li giti" - she is forbidden to eat immediately:
If she told the agent "Hiskabel li giti" - "Receive my get for me" - he is an agent for receipt, and from the moment the get reaches the agent's hand she is divorced. She is therefore forbidden to eat Terumah immediately, since perhaps the agent received the get the moment he stepped out the door, and she was divorced at that very hour.
"Hiskabel li giti bemakom peloni":
The mishnah's wording is "ochelet biTerumah ad sheyagia haget le'oso makom" - "she eats Terumah until the get reaches that place." At first glance this suggests that the agent must receive the get in the place she specified, but the Gemara explains that this is not the mishnah's intent. Its intent is that even if the agent received the get elsewhere, it is not a valid get until he brings it to that place - and this is the meaning of "until the get reaches that place," that he must carry it there.
The difficulty:
In the previous mishnah we learned, according to the first Tanna, that when the woman stipulates and asks that the get be received specifically in a particular place, the get takes effect only if the agent received it in that place. Here, however, it is stated that the get takes effect when it arrives at that place, even though it was received somewhere else. Yet from the designating language she used it would seem that it is not a get unless the agent took it in that very place.
The Gemara's resolution:
The Gemara explains that our mishnah is speaking of a woman who said: "Receive my get for me in such and such a place, but my husband is sometimes found elsewhere." From this wording we hear that she is not particular about where the get is actually received; and when she said "in such and such a place," she meant that even if the agent receives it elsewhere, it will not be considered a valid get until it arrives at that place. Her insistence, then, is not upon the place of receipt, but upon the get not taking effect until it comes to that place.
The view of Rabbi Eliezer:
The mishnah concludes with the view of Rabbi Eliezer, who follows his position in the previous mishnah and forbids immediately: in his words the woman is forbidden to eat Terumah at once, and the matter does not depend at all on calculating the time at which the get will reach that place, for the get takes effect immediately. In his view the woman has no power to be particular either about the place where the get is received or about the place to which it is brought, and therefore her statement that she wants it to be a valid get only in a particular place has no consequence whatsoever. The reason: since the woman is divorced against her will, she has no power to stipulate or be particular in these matters.
In summary: We learned three cases regarding eating Terumah - when she says "Bring me my get" she eats until the get reaches her hand, since the language of agency is not the language of one's own hand; when she says "Receive my get for me" she is forbidden immediately, since perhaps the agent has already received the get; and when she says "Receive my get for me in such and such a place" she eats until the get reaches that place, and according to the Gemara's explanation her insistence is not upon the place of receipt but upon the place where the get takes effect. Rabbi Eliezer, consistent with his position, forbids immediately, for the woman has no power to be particular about this, since she is divorced against her will.