פרשת בהר תשל"א - איסור ריבית

And these people violate a prohibition of interest: The lender, and the borrower, and the guarantor, and the witnesses. And the Rabbis say: Also the scribe who writes the promissory note violates this prohibition. These parties to the transaction violate different prohibitions. Some are in violation of: “You shall not give him your money with interest” (Leviticus 25:37), and of: “Do not take from him interest or increase” (Leviticus 25:36), and of: “Do not be to him as a creditor” (Exodus 22:24), and of “Do not place interest upon him” (Exodus 22:24), and of: “And you shall not place a stumbling block before the blind, and you shall fear your God; I am the Lord” (Leviticus 19:14).

"And if thy brother be waxen poor, and his means fail with thee; then thou shalt uphold him"

והחזקת בו THOU SHALT RELIEVE HIM — Do not leave him by himself so that he descends and falls, when it will be difficult to give him a lift, but uphold him from the very moment of the failure of his means. To what may this (the differences between whether you assist him at once or whether you wait with your help till he has come down in the world) be compared? To an excessive load on the back of an ass. So long as it is still on the ass’s back, one person is enough to take hold of it (the load) and to keep it (the ass) up, as soon as it has fallen to the ground not even five persons are able to set it on its legs (Sifra, Behar, Section 5 1).

That which it says, "Do not take from him," implies that it is permitted to take from the wealthy. Likewise in Parshat Mishpatim (Exodus 22:24), it states, "If you lend money to My people, to the poor among you... exact no interest from him." Hence the Torah wrote in Deuteronomy 23:21, "Do not take interest from your brother" - do not take interest from anyone who is your brother, and even though the borrower profits from it. For the main reason for the prohibition of interest is because it erodes the trait of trust [in God]. As anyone engaged in business has his eyes lifted towards God, since he is in doubt whether he will make a profit or not. But one who gives with interest has his profit known and designated. So he will rely on his surety and remove his heart from God. And that which the borrower also transgresses the negative commandment is because he causes the creditor to sin and erodes his trait of trust. This is known from [observing] those that lend with interest. As most of them have little faith, and are 'stubborn-hearted and distant from charity' because of their lack of trust in God. This is the reason for the prohibition of interest in every place...

"Thou shalt not give him thy money upon interest, nor give thy victuals for increase."

And it mentioned the word, "interest (literally, bite)," [as well as] "increase"; as it is called, "bite," to the borrower, since it is is similar to [the bite of] a snake - in the way that if it bites his heel, it results in a small scratch; but it [then] proceeds to rise and swell to his skull. At first, it is not noticeable until its fever rises and cannot be cured. But to the creditor, it is called increase, as it increases his wealth and property...