Parshas Ki Setzei
“You shall not give interest to your brother be it interest of money, interest of food or interest of anything which can be made into interest (for a loan)!” (Devarim 23:20)
It is a negative commandment that we may not give interest to a Jew, nor may we accept interest from a Jew, and about this it says “You shall not give interest to your brother be it interest of money, interest of food or interest of anything which can be made into interest (for a loan)!”. The Torah needed to write this explicitly so that we would not think that the prohibition is only incumbent on the lender that he should not take interest, but that if the borrower decides of his own accord to give interest we might think that it might be permitted. It is for this reason that the Torah warns us explicitly that this is also included in the prohibition.
Amongst the roots of this prohibition are that Hashem in His goodness wanted to ensure that his chosen people should be able to live. He therefore commanded them to remove all stumbling-blocks from their paths so that no member of the nation would be able to swallow up the money of his friend without the other even realizing to the extent that his house would end up empty of everything good, for such is the way of interest. This is well-known and it is for this reason that it is called “Neshech” (which normally means biting).