To make one bigger coin. Masechet Eduyot, Perek Alef, Mishnah Tet. The next two mishnayot (Mishnahs) to talk about are about ma'aser sheni (second tithe). All produce grown in Eretz Yisrael has to have different portions separated from it. One of them is ma'aser sheni, where the produce designated as ma'aser sheni has to be brought to Yerushalayim (Jerusalem) and eaten there. If it's too burdensome for a person to bring all the produce he has to Yerushalayim and eat it there, he could transfer the holiness of the ma'aser sheni fruits onto money. If he has a selah—that's a denomination of a coin, worth of ma'aser sheni—he could transfer its holiness onto a selah coin. He then takes that coin to Yerushalayim and uses it there to buy food and drink and enjoy himself in Yerushalayim. We'll talk here about ma'aser sheni that's on smaller coins, because he transferred it from the vegetable onto the smaller coins. Now he wants to transfer the sanctity from those coins onto larger coins in order to bring fewer coins with him to Jerusalem.
The Mishnah says that if someone has copper coins of ma'aser sheni and wants to exchange the many copper coins he has for one silver coin, Beit Shammai omrim—Beit Shammai says, “You're allowed to do it.” You could change all of your copper coins to the value of a selah, a silver selah coin. You're allowed to do that. It makes it easy for you to go up to Jerusalem with one bigger coin, as opposed to all of those smaller coins. That's allowed. Beit Hillel omrim—Beit Hillel says you're allowed to exchange half of the copper coins, which is the value of a shekel. A shekel is half of a selah, so we'll call it half a silver coin. You could take half of your copper coins and exchange them for a shekel, which is half of a selah. But you keep the other half of the copper coins, which are also worth another shekel, or half a selah, as copper coins.
The reason being, when a person gets to Yerushalayim with all of his ma'aser sheni money, he's going to want to buy something small here and there to enjoy. He's going to want to buy an ice cream cone or a drink, and the copper coins are what he uses for those smaller purchases. You don't use a $100 bill, for example, to buy a $2 ice cream. That doesn't work. Especially during the ma'aser sheni season, when people are all coming up to Yerushalayim at the same time for the holidays, if everybody brought those bigger denominations, those very expensive coins, they would want to exchange them for copper coins to make smaller purchases. There'd be a run on the bank. Everybody would go there, and everybody would want to exchange their coins all at once. There'd be a tremendous, tremendous demand for copper coins. Therefore, the price of copper would rise. If the price of copper rises, a person isn't going to get as much as he could have gotten if the price stayed the same. He's not going to get as much bang for his buck. Eating this food is a mitzvah (commandment), so Beit Hillel wants to make sure you're going to get as much food as you can with the money you're bringing with you. That's why Beit Hillel says you have to keep half of your ma'aser sheni money in copper coins, to make sure there's not a crazy demand once everyone arrives in Yerushalayim.
Another machloket (dispute) about ma'aser sheni: Rabbi Meir says you're not allowed to transfer together the holiness of ma'aser sheni money and ma'aser sheni produce to make one larger silver coin. For example, let's say you have ma'aser sheni coins worth half of a dinar (coin) and ma'aser sheni produce worth half of a dinar. You're not allowed to say, “You know what? Let me take the holiness of both of them. I'll put them both onto one bigger silver dinar coin.” Both of them, the money and the produce, will lose their holiness. Let's try that. But Rabbi Meir says you're not allowed to do that. A transfer of ma'aser sheni is only allowed if it's distinct, if it's not mixed together with another transfer. So when you have money and produce trying to go in tandem in order to have the holiness to make one bigger item, that's not allowed to be done. It's not allowed to be transferred. It's not allowed to be transferred together. But Chachamim (Sages) allow this type of transfer, but with a certain nuance to it. Everybody agrees. Chachamim agree with Rabbi Meir that when you have enough coins over there, nobody would say that you're allowed to do a mixed transfer to combine the two for one bigger coin. If you have enough coins for them to produce their own bigger coin, you're not allowed to do anything. But the mixed transfer that Chachamim allow is only if you don't have enough coins to produce a bigger coin and don't have enough produce to produce a bigger coin. Only with the combination of the two could you get that bigger denomination. For example, let's say you have half of a dinar's worth of produce and half of a dinar's worth of small coins. Only in that scenario would Chachamim say that you're allowed to transfer each of them onto one bigger coin. That would be allowed. But if you had enough for a full dinar and another full dinar, you wouldn't be allowed to cross-transfer the produce and the funds to make one bigger coin.