פירוש על ויקרא 25:37

את כספך לא תתן לו בנשך, "You shall not give him your money upon interest;" Here the Torah explains what the words נשך ומרבית are all about; they darken the divine light G'd provides. The word את כספך refers to the material things man yearns for in this world believing them to be of real value though their value is totally illusory. לא תתן לו בנשך When man fulfils his animalistic instincts and thereby tries to gratify his spiritual needs his spirit is actually "bitten," נשוך and the poison of sin is absorbed by that person's רוח. The Torah continues: ובמרבית לא תתן אכלך, "and you must not give him your food in return for increase." The Torah means that even your food, i.e. something that it is certainly permissible for you to eat you must not consume to excess, i.e. מרבית. When a person follows the needs of his palate he gradually increases his appetite for more food than is needed to sustain him. This is turn also leads to the divine light G'd has granted us by means of our pure soul being gradually more and more "blacked out." The stronger the physical in man the weaker his spiritual capacity. Encouraging the body to grow stronger through gratifying its appetites therefore is sinful. This is why Proverbs 13,25 teaches us that "the righteous eats onIy to satisfy the needs of his life-force, נפש." Solomon says this to remind us that it is not our palate which should dictate the quantity or quality of our food-intake. When the Torah continues אני השם (verse 38), this means that although G'd has taken us out of Egypt in order to give us the land of Canaan, the purpose was not in order for the Jewish people to stuff themselves on the good fruit of the land but in order for Him to be our G'd, something that requires the land of Israel. Our sages in Torat Kohanim say that anyone who merely lives in the land of Israel is as if he had accepted for himself G'd's sovereignty.

נשך ותרבית, “outright interest, or food against repayment by a greater amount, etc.” Nachmanides writes that according to the plain meaning of he text it appears that נשך refers to a loan to be repaid with a fixed amount of interest which runs and is payable concurrently. It is called נשך, “bite,” as the borrower feels as if he is being bitten every time he makes an interest payment. The word תרבית refers to a loan of money for a fixed period at the end of which both principal and interest is due. Seeing that the “interest” does not accumulate even when the principal is repaid after the agreed upon time, the Torah does not describe such a transaction as נשך. מרבית, on the other hand, refers to loans of food or other chattels, not loans of money. Here too the Torah forbids the lender to charge any extra when the harvest time rolls around and the borrower repays him from the new harvest.

את כספך, “your money;” the emphasis is on the pronoun “your; it is perfectly legal to lend money at interest when it is a gentile’s money. (A Jewish bank administering funds deposited by a gentile, may charge a Jew interest for such loans.)