We begin our study of Maseches Avodah Zarah, chapter 1, mishnah 1. The opening topic of the tractate is our relationship with idolatrous society, and specifically how to conduct ourselves around their pagan festivals. The central concern of the opening mishnah is this: when an idolater's festival approaches, and he is about to celebrate and even bring an offering to his idol, he is likely to praise that idol for the good things that have happened to him. It turns out that a Jew who does business with him or benefits him just before his festival gives him a reason to thank his idol and to credit it with those good events - and that is forbidden.
The basis of the prohibition:
This is a rabbinic prohibition. In Shemos chapter 23, verse 13 it says: "and the name of other gods you shall not mention, it shall not be heard on your mouth." Although the plain meaning of the verse refers to a Jew causing a non-Jew to swear by the name of his idol, the Sages extended it to include mentioning the idol's name merely by way of praise, without any oath. The mishnah therefore establishes rules limiting a Jew's interaction with an idolater around his festival, so that he will have no reason to mention his idol's name and praise it.
"Lifnei eideihen shel ovdei kochavim sheloshah yamim" - for three days before the festivals of idolaters:
The word "eideihen" is not a common word. "Eid" with an aleph appears in Parashas Haazinu in Sefer Devarim: "karov yom eidam" - the day of their downfall is near. "Eid," then, expresses ruin and disaster, and the mishnah deliberately chose this term for their pagan festival as a term of derision.
The three days are counted before the festival itself. For example, if the festival falls on the fifteenth of the month, the prohibition applies on the twelfth, the thirteenth and the fourteenth of the month - and on the fifteenth itself, of course.
These are the specific prohibitions the mishnah lists:
"Asur laseis velaseis imahem" - it is forbidden to do business with them, to buy from them or sell to them, lest the idolater attribute his financial success to his idol and praise it.
"Lehashilan velisho'ol mehen" - it is forbidden to lend him an object, since he will then have something in hand that gives him pleasure; and it is also forbidden to borrow from him, since he will be pleased that he has a measure of control over Jews and that they depend on him.
"Lehalvosan velilvos mehen" - it is forbidden to lend them money or to borrow from them, for the same reason. It is worth noting that lending with interest is permitted, since in that case they take no pleasure in the financing.
"Lefor'an ulehipara mehen" - it is forbidden to repay a debt to them, since that enriches them, and it is also forbidden to collect a debt from them. Although at first glance collecting reduces his money, in the end he will be glad that he is no longer burdened by the debt, and he will credit that gladness to his idol, giving him a reason to give thanks.
The Bartenura qualifies this and explains that even if this law were to apply in practice - and as will be explained below it does not - the mishnah does not come to forbid collecting a debt that is not enforceable. That is, when the Jew does not hold an enforceable contract, he may collect his debt during this window of time, since the alternative is that he will never collect it at all, and we do not require a Jew to lose his money because of a rabbinic concern that the non-Jew might praise his idol. But when he does hold an enforceable loan contract - that is the case the mishnah is discussing, and he may not collect, since he will be able to collect it at a later date.
The dispute between Rabbi Yehudah and the Sages:
"Rabbi Yehudah omer, nifra'in mehen" - Rabbi Yehudah says we may collect from them. In Rabbi Yehudah's view it is permitted to collect the debt from the idolater, because it distresses him: repaying the debt reduces his money and saddens him, and it will not lead him to praise his idol.
The Sages, however, disagree with him and say: "Af al pi shemeitzer hu achshav" - even though he is distressed now. True, at that moment it pains him to return the money he owed, but a short while later he will be glad that he is no longer shackled by the debt, and therefore it is forbidden.
The halachah, then, is that even on the day of the festival itself one may not collect a debt from an idolater, because an hour or two later, while he is still in the midst of his festival, he will attribute his relief from the burden of the debt to his idolatry and will praise it by name - and we must not be the cause of that happening.
In summary: In this Mishnah we learned that the three days before the festivals of idolaters, and the day of the festival itself, are forbidden for buying and selling, for lending and borrowing articles, for lending and borrowing money, and for repaying debts and collecting them - all out of concern that the idolater will attribute the good fortune that came his way to his idol and praise it, in violation of the prohibition of "ve'shem elohim acheirim lo yishama al picha" - "and the name of other gods shall not be heard from your mouth." We noted the Bartenura's qualification regarding a debt that cannot be enforced, and the dispute between Rabbi Yehudah and the Sages concerning collection, which was decided in accordance with the Sages.