The severity of the prohibition against lending money at interest is well-known, as one transgresses five negative commandments and one’s property loses value and he descends and does not come back up, nor does he have any portion in the G-d of Klal Yisrael, and does not rearise at the revival of the dead. There are people who do not realize the severity of this prohibition or they think that since Chazal permitted it through the use of a “Heiter Iska” (Document changing the loan into a business deal), that it is permitted even without one, and they are not learned in the details of the prohibition and are often caused to commit this crime.
One whose fear of heaven touches his heart, if he knows that he has in his hand money from interest on a loan should hurry and return it before he loses the permissible money in his hand because of the sin of holding forbidden money. One who fears Hashem and wants his money to be guarded should go to a wise man and learn from him all of the laws of interest so as not to commit this sin by error.
A person should tremble and be afraid of this sin and make sure that the prohibition of interest should not touch his money more than he is afraid of the prohibited pig’s meat or blood should not touch his food, as it is actually more severe. One who eats pig’s meat or blood etc., transgresses one negative commandment whereas with lending at interest one transgresses five negative commandments.