(Devarim 23:21) "To the stranger shall you give interest, but to your brother shall you not give interest": "to the stranger shall you give interest" — a positive commandment; "but to your brother shall you not give interest — a negative commandment.
R. Gamliel says: What is the intent of "but to your brother shall you not give interest"? It is already written (Ibid. 20) "You shall not give interest to your brother" — There is antecedent interest and supervening interest. How so? If he thought to borrow from him and sent him (a gift), thinking "So that he lend me," this is antecedent interest. If he borrowed from him and returned his money and sent him (a gift), thinking "For his money that was 'idle' with me," this is supervening interest.
"so that the L-rd your G-d will bless you in all to which you put your hands": Scripture "established" for him a blessing in all the sending forth of his hands.
(דברים כג כא) לַנָּכְרִי תַשִּׁיךְ וּלְאָחִיךָ לֹא תַשִּׁיךְ, לַנָּכְרִי תַשִּׁיךְ מִצְוַת עֲשֵׂה. וּלְאָחִיךָ לֹא תַשִּׁיךְ, מִצְוַת לֹא תַעֲשֶׂה.
(Devarim 23:21) "To the stranger shall you give interest, but to your brother shall you not give interest": "to the stranger shall you give interest" — a positive commandment; "but to your brother shall you not give interest — a negative commandment.
רַבָּן גַּמְלִיאֵל אוֹמֵר: מַה תַּלְמוּד לוֹמַר וּלְאָחִיךָ לֹא תַשִּׁיךְ, וַהֲלֹא כְּבָר נֶאֱמַר לֹא תַשִּׁיךְ לְאָחִיךָ, אֶלָּא יֵשׁ רִבִּית מֻקְדֶּמֶת וְיֵשׁ רִבִּית מְאֻחֶרֶת. כֵּיצַד? נָתַן עֵינָיו לִלְווֹת מִמֶּנּוּ וְהָיָה מְשַׁלֵּחַ לוֹ וְאוֹמֵר בִּשְׁבִיל שֶׁיַּלְוֶנּוּ – זֶה הוּא רִבִּית מֻקְדֶּמֶת; לָוָה הֵימֶנּוּ וְהֶחֱזִיר לוֹ מְעוֹתָיו וְהָיָה מְשַׁלֵּחַ לוֹ וְאוֹמֵר בִּשְׁבִיל מָעוֹתָיו שֶׁהָיוּ בְּטֵלוֹת אֶצְלִי – זֶה הוּא רִבִּית מְאֻחֶרֶת.
R. Gamliel says: What is the intent of "but to your brother shall you not give interest"? It is already written (Ibid. 20) "You shall not give interest to your brother" — There is antecedent interest and supervening interest. How so? If he thought to borrow from him and sent him (a gift), thinking "So that he lend me," this is antecedent interest. If he borrowed from him and returned his money and sent him (a gift), thinking "For his money that was 'idle' with me," this is supervening interest.
לְמַעַן יְבָרֶכְךָ ה׳ אֱלֹהֶיךָ בְּכֹל מַעֲשֵׂה יָדֶיךָ, קָבַע לוֹ הַכָּתוּב בְּרָכָה בִּשְׁלִיחוּת יָד.
"so that the L-rd your G-d will bless you in all to which you put your hands": Scripture "established" for him a blessing in all the sending forth of his hands.
עַל הָאָרֶץ אֲשֶׁר אַתָּה בָא שָׁמָּה לְרִשְׁתָּהּ, בִּשְׂכַר שֶׁתָּבֹא תִּירַשׁ.
"on the land whither you are coming to inherit it": in reward for your coming, you will inherit.