לַנָּכְרִ֣י תַשִּׁ֔יךְ וּלְאָחִ֖יךָ לֹ֣א תַשִּׁ֑יךְ לְמַ֨עַן יְבָרֶכְךָ֜ יְהוָ֣ה אֱלֹהֶ֗יךָ בְּכֹל֙ מִשְׁלַ֣ח יָדֶ֔ךָ עַל־הָאָ֕רֶץ אֲשֶׁר־אַתָּ֥ה בָא־שָׁ֖מָּה לְרִשְׁתָּֽהּ׃ (ס)
Unto a foreigner thou mayest lend upon interest; but unto thy brother thou shalt not lend upon interest; that the LORD thy God may bless thee in all that thou puttest thy hand unto, in the land whither thou goest in to possess it.
Read kabbalistic (mystical) interpretation of Deuteronomy 23:21: and classical mystical sources.