Even though usually אם is optional, the Mechilta says that there are three examples where it is imperative, with this being one of them. One must lend; lending is a mitzvah. The Chafetz Chaim tells us ...

When we consider whether or not someone is an observant Jew, we usually ask whether he or she is shomer Shabbos. Why is this the defining feature of religious observance? What makes Shabbos a root mit ...