Deuteronomy 23:20 - Matthew Poole's English Annotations on the Holy Bible

Unto a stranger, i.e. to a person of any other nation, for so that word is generally used, and therefore they who restrain it to the cursed Canaanitish nations seem to do so without any solid or sufficient grounds. And though the word brother is ofttimes used in a general sense for every man, yet I think I may affirm that wheresoever the words brother and stranger are opposed in the Jewish law, the brother signifies the Israelite only, and the stranger signifies any person of what nation or religion soever, whether proselyted to the Jewish religion or not, and so it seems to be meant here. And the reason why usury is permitted to a stranger, not to an Israelite, may seem to be this, because the Israelites generally employed themselves in the management of land and cattle, and therefore could not make any advantage of borrowed money to balance the use they should pay for it; and consequently it may be presumed that they would not borrow money upon use, but for want and poverty, and in that case, and principally for that reason, usury seems to be forbidden to them, as may be thought from Leviticus 25:35,36. But the strangers made use of their money in way of trade and traffic with the Israelites, which was more gainful, and could much better bear the burden of usury, and reap advantage from money so borrowed; and these strangers here spoken of are supposed to be competently rich, and not poor, as may plainly appear by comparing this place with Leviticus 25:35,36, where they are no less forbidden to take usury of a stranger than of a brother, in case of poverty.