in which he instructs that taking interest from a non-Jewish poor person is forbidden, for he is to be considered a sojourner, whom we are commanded to sustain
"…but you may deduct interest from loans to foreigners. Do not deduct interest from loans to your countrymen." A non-Jew residing in the Land of Israel is called a sojourner, we are commanded to sustain them; they are not considered idol-worshippers. Should a non-Jew, however, who comes and goes only for commerce - such as to buy grain to sell in other lands - wish to purchase and pay later, after their return…it is permissible to take interest from them, since they are earning a profit from commerce, in keeping with the laws among all nations – that the lender takes interest for the use of the money, which lay idle. "Do not deduct interest from loans to your countrymen". The people of Israel were not merchants, and worked the land for their livelihood, selling only surplus to foreigners. Borrowing was done only out of distress… But now that Jews deal in commerce, it seems permissible to deduct interest from them, but not from the poor. Similarly with the non-Jew, if they are involved in commerce, it is permissible to deduct interest from them, but if they are poor – it is forbidden to deduct interest from them, for their case is not similar to the one referred to in the Torah. They live among us and are therefore like the sojourner whom we are obliged to sustain; if the Torah has mercy on the sojourner living among us, it has all the more on the non-Jews among whom we are sojourners. But now that Jews deal in commerce, it seems permissible to deduct interest from them, but not from the poor. Similarly with the non-Jew, if they are engaged in commerce, it is permissible to deduct interest from them, but if they are poor – it is forbidden to deduct interest from them, for their case is not similar to the one referred to in the Torah. They live among us and are therefore like the sojourner whom we are obliged to sustain; if the Torah has mercy on the sojourner living among us, it has all the more on the non-Jews among whom we are sojourners.
Commentary on the Five Books of Torah, Ki Tezeh weekly reading portion, pp. 545-546, Jerusalem, 1993