Sheviis, Chapter 8, Mishnah 4. We mentioned earlier that when a person sells produce of Sheviis - even in a permitted manner - the money he receives in exchange takes on the sanctity of Sheviis produce. Our Mishnah comes to distinguish between what is considered payment for Sheviis produce and what is nothing more than wages for labor.
Wages of a worker for gathering vegetables:
"Ha lecha issar zeh u'lekot li yarak hayom" - "Here is this issar for you, and gather vegetables for me today." The issar he gave him was given purely as his wage. It is not considered money of Sheviis produce, since it was not exchanged against the value of the Sheviis crop, but rather is payment for the work itself, the cost of the effort. His wage is therefore permitted, and it does not carry the sanctity of Sheviis.
"Lekot li bo yarak hayom" - "Gather vegetables for me today with it." Here he told him to pick with the money he is giving him, and therefore his wage is forbidden, meaning that it carries the sanctity of Sheviis. In this manner he is not hiring him for his labor, but rather buying from him what he picks.
One who buys a loaf from a baker:
If a person takes a loaf of bread from a baker for a pundyon and says to him: when I gather field vegetables I will bring you some - this is permitted. Those vegetables are ownerless, and the one gathering them is merely saving the baker trouble and doing him a favor through the effort of gathering. Even though this takes place in the Shemittah year, it is permitted, since we do not view those vegetables as payment, but rather as two people giving each other free gifts that are not necessarily connected to one another: one gives a loaf worth a coin, and the other does him a favor and brings him from what he gathered in the field.
However, if he took the loaf from him without any such arrangement, and now owes him money for the loaf - "Lo yeshalem ela midmei Sheviis" - he may not pay him from money of Sheviis; that is, he cannot settle his debt with Sheviis money, "she'ein por'in chov midmei Sheviis" - for one does not pay off a debt with money of Sheviis. Paying off a debt with Sheviis money is considered doing business and trading in Sheviis produce, and that is forbidden.
In the case we permitted here, where he took a loaf from the baker for a pundyon, a clarification is needed: he is not telling him that he is buying it for a payment of a pundyon; rather, the pundyon is an indication of the size of the loaf.
In summary: in this Mishnah we examined the distinction between wages for labor and money paid for Sheviis produce - "u'lekot li" as opposed to "lekot li bo"; the permission for one who takes a loaf from the baker, as two parties doing each other a favor rather than exchanging payment; and the rule that one does not pay off a debt with money of Sheviis, because that is considered trading in Sheviis produce.