Behar - Chamishi
A Lack of Interest
There's a difference between a field and a building. If someone sells developed property in a walled city, it can only be redeemed for one year. If it's not redeemed by the end of the year, it becomes the permanent property of the buyer. Such property does not revert back in the Jubilee year. Houses in open towns, however, are treated the same as fields.
The Leviim were to be assigned particular cities throughout the land. Buildings in these could be redeemed and would revert back in Yoveil, even though the cities were walled.
G-d says that when a person suffers financial hardship, there is an obligation to help him get back on his feet. This applies equally to helping converts and those born Jewish. Accordingly, charging interest is forbidden, as it goes counter to the concept of helping one another.
Charging interest is a serious offense; one may not even voluntarily pay interest or co-sign a loan between Jews involving interest. However, this law only applies among Jews. Jews may charge interest to non-Jews and may be charged interest by non-Jews. (This relationship between Jews and non-Jews is fair in that neither side has the exclusive ability to charge interest of the other.)