Abaye says: No, actually, the baraita is referring to an unblemished animal when the Temple is standing, but it is speaking of a firstborn offering outside of Eretz Yisrael, and it is in accordance with the opinion of Rabbi Shimon, who said: If unblemished firstborn offerings came from outside of Eretz Yisrael, they may be sacrificed on the altar. This language indicates that there is no obligation to sacrifice such an animal, as people did not generally bring their firstborn offerings from outside Eretz Yisrael. Therefore, a priest is able to acquire it even when it is unblemished. Firstborn offerings from Eretz Yisrael, by contrast, cannot be acquired by the priests.

§ The Gemara raises an objection from the mishna: Rabbi Yoḥanan ben Nuri said to him: What is this comparison for me? If a priest does not substitute for a sin offering and a guilt offering, which priests do not acquire during the animals’ lifetimes, will you say the same with regard to a firstborn, which priests acquire during the animal’s lifetime? What are we dealing with in the mishna? If we say that it is referring to a blemished animal, isn’t the mishna saying that the firstborn offering is similar to a sin offering and a guilt offering, which the priests acquire only unblemished? Rather, is it not referring to unblemished animals? And it nevertheless teaches: Which priests acquire during the animal’s lifetime.

Ravina said: This mishna too is referring to a firstborn offering outside of Eretz Yisrael, and it is in accordance with the opinion of Rabbi Shimon, who said: If unblemished firstborn offerings came from outside of Eretz Yisrael, they may be sacrificed on the altar. The priests do not acquire firstborn offerings from Eretz Yisrael.

The Gemara suggests: Let us say that acquisition of the firstborn offerings by the priests is the subject of a dispute between tanna’im. The baraita states: In the case of a firstborn offering, when it is in the house of its owner, who did not yet give it to a priest, its owner can render another animal a substitute for it. Once it is in the house of the priest, its owner cannot render a substitute for it. Rabbi Shimon ben Elazar says: Once it has entered the possession of the priest, its owner cannot render a substitute for it.

Apparently, the opinion of Rabbi Shimon ben Elazar is identical to that of the first tanna. What is their dispute? What, is it not correct that this is what the first tanna is saying: Once it is in the house, i.e., possession, of the priest, the priest can render a substitute for it, but the owner cannot render a substitute for it, as the priest has acquired it; while Rabbi Shimon ben Elazar holds that once it enters the possession of the priest, neither of them can render a substitute with it. Apparently, the first tanna holds that the priest has the right of acquisition to an unblemished firstborn offering when the Temple is standing.

The Gemara explains: The opinion of the first tanna is not difficult; one can say that the dispute in the baraita concerns a firstborn offering outside of Eretz Yisrael, while those from Eretz Yisrael are not acquired by the priests. And this opinion of the first tanna accords with the opinion of Rabbi Yoḥanan ben Nuri in the mishna above, and that opinion of Rabbi Shimon ben Elazar accords with the opinion of Rabbi Akiva in that mishna.

§ The Gemara earlier (7b) cited a mishna (Ma’aser Sheni 1:2) which states that a firstborn offering may be sold unblemished only while it is alive. Rav Ḥisda says: The Sages taught this halakha only with regard to a priest selling to a priest, but with regard to a priest selling it to an Israelite, it is prohibited even when the animal is alive. What is the reason? Since an Israelite can consume a firstborn animal only if it is blemished, there is a concern that perhaps the Israelite will go and inflict a blemish on the firstborn offering and bring it to a halakhic authority to attain permission to eat it, and he will say to him: A priest gave me this firstborn offering when it was already blemished.

The Gemara asks: And may a halakhic authority permit the animal in a case such as this? But didn’t Rav say: A halakhic authority may not look at a firstborn offering brought by an Israelite to determine if it has the type of permanent blemish allowing it to be slaughtered unless a priest is with him, out of concern that the Israelite will keep the blemished animal for himself without performing the mitzva of giving it to a priest? If so, one can demand that the priest who sold him the animal must be present, and this should prevent the Israelite from lying about the blemish.

Rav Huna, son of Rabbi Yehoshua, said: This is the reason why it is prohibited for a priest to sell an unblemished firstborn offering to an Israelite: Because this looks like a priest who assists at the threshing floor in order to receive teruma from an Israelite. Unblemished firstborn offerings have a low purchase price, as the owner must wait for it to become blemished before eating it. It might appear that the priest sold the animal to an Israelite at a discount in order to receive future firstborns from him.

The Gemara relates: Mar Zutra arrived at the home of Rav Ashi. Those present said to him: Let the Master taste some food. They brought meat before him. The one who placed the meat before him said: Let the Master eat, as this meat is particularly healthful, because it is a firstborn. Mar Zutra asked: From where did you receive this firstborn animal? They said to him: It is an animal that so-and-so the priest sold to us.

Mar Zutra said to them: Do you not hold like that which Rav Huna, son of Rabbi Yehoshua, said, that Israelites may not receive an unblemished firstborn offering from a priest because it looks like a priest who assists at the threshing floor? They said to Mar Zutra: We hold that this is not a concern, as we purchased it for its fair market value, and did not receive it at a discount. Therefore, there is no appearance of impropriety.

Mar Zutra said to them: But do you not hold like that which we learned in a mishna (Bekhorot 26b): Until when is an Israelite obligated to tend to a firstborn animal before giving it to the priest? In the case of a small animal, a sheep or goat, thirty days, and in the case of a large animal, one of a herd of cattle, fifty days. And if the priest said to the owner: Give it to me within its period, the owner may not give it to him. And Rav Sheshet says: What is the reason for this? Because it looks like a priest who assists at the threshing floor, as the priest is assisting the Israelite by assuming the responsibility of tending to the firstborn.

They said to Mar Zutra: There the circumstances of the matter prove that the priest accepted responsibility to care for the animal in return for some benefit, and it has the appearance of impropriety. Here, we purchased it for its fair market value, and there is no appearance of impropriety.

The Gemara presents an alternative version of this final response. They said to Mar Zutra: There the Israelite does not give payment to the priest for accepting responsibility to care for the animal. Here, the Israelite gives payment to the priest, as we purchased the animal. And what would you say to this claim? Would you say that perhaps the priest lowered the price of the animal for us, as the priest thinks that when we have another firstborn offering we will give it to him, and therefore it has the appearance of impropriety? This is not a concern, as he thinks: