In this week’s parshah the Torah tells us some of the halachos of collecting debts. There is a question that the achronim ask on the obligation to repay a debt. The Gemara in Kesubos 86a says that it is a mitzvah to repay one’s debts. The Gemara in Kesubos 50a says that one should not spend more than one fifth of his wealth on performing a mitzvah. This halacha is codified in the Shulchan Aruch by the Rema in siman 556. Why then is one obligated to repay a debt that is more than one fifth of his wealth?
The Be’er Halacha (656 d”h afilu) explains the logic behind the spending limit of a fifth of one’s wealth on mitzvos. He explains that this limit was set in order to prevent one from giving away too much of his money – and as a result become needy and be forced to rely on others. In a situation where half a shekel is more than one fifth of one’s wealth, he is already needy and already relies on others. Since giving the machatzis hashekel will not change his financial situation, he is obligated to do so even though it is more than a fifth of his income.
Rav Moshe Feinstein (Dibros Moshe Kiddushin 30b and Igros Moshe Orach Chaim 5:41) explains that one is not exempt from performing any mitzvos, even if they cost more than a fifth of his wealth. He explains that there are two types of mitzvos. One type is when the mitzvah is to spend money, i.e. pidyon haben, or repaying a debt. In the mitzvah of pidyon haben the Torah obligates one to pay the kohen money to redeem his son.
The second type of mitzvah is performed with an item, i.e. esrog. With the latter, the money spent on obtaining that item is not part of the mitzvah. When one does not have the item required to perform a mitzvah, he must try to obtain it. Should such items be unavailable, he will be exempt from performing that mitzvah. The rule that one is not required to spend more than a fifth of his wealth on a mitzvah applies only in this type of mitzvah, where the spending is not part of the mitzvah, but rather a means of obtaining the mitzvah. Since one is not obligated to spend more than a fifth, if the mitzvah will cost more than a fifth we consider it as if the item is unavailable. The rule that one need not spend more than a fifth of his wealth on a mitzvah is not an exemption to performing any of the mitzvos; it can merely render an item unavailable for purchase.
On the other hand, regarding a mitzvah in which the actual spending is the mitzvah, and there is nothing to be purchased for the mitzvah, there is no exemption. He must spend the money even if it will cost more than a fifth of his wealth, for that is what the Torah has obligated us to do. In the mitzvah of machatzis hashekel, the Torah obligated us to spend half a shekel regardless of whether it will cost more than a fifth. Similarly, the mitzvah of repaying a debt is a commandment to pay money, and therefore one must pay even if it costs him more than a fifth of one’s wealth.
The following scenario signifies the difference between the ruling of the Be’er Halacha and that of the Igros Moshe: A poor man who is currently not reliant on others for his finances. If he becomes obligated in the mitzvah of pidyon haben, and the five selaim needed for the mitzvah amounts to more than a fifth of his wealth. According to the Igros Moshe, he would not be exempt from the mitzvah, for the mitzvah is to spend the money. The Be’er Halacha would disagree, however, and exempt the man from the mitzvah, since by spending money for this mitzvah he will become needy and reliant on others.
Another difference is in a scenario where one makes enough money that spending more than one fifth of one’s wealth will not put him in a predicament where he would become needy. According to the Mishnah Berurah he would be allowed to spend more than a fifth of his wealth on a mitzvah. However, according to Rav Moshe one would never be obligated to spend more than one fifth of his wealth on a mitzvah, provided that it is a mitzvah that is not directly an obligation to pay.