יִפְתַּ֣ח יְהוָ֣ה ׀ לְ֠ךָ אֶת־אוֹצָר֨וֹ הַטּ֜וֹב אֶת־הַשָּׁמַ֗יִם לָתֵ֤ת מְטַֽר־אַרְצְךָ֙ בְּעִתּ֔וֹ וּלְבָרֵ֕ךְ אֵ֖ת כָּל־מַעֲשֵׂ֣ה יָדֶ֑ךָ וְהִלְוִ֙יתָ֙ גּוֹיִ֣ם רַבִּ֔ים וְאַתָּ֖ה לֹ֥א תִלְוֶֽה׃
Otworzy ci Wiekuisty skarbnicę Swą dobroczynną, - niebo, aby dać deszcz ziemi twej w czasie swoim, i by błogosławić wszelkiej sprawie rąk twoich, że będziesz wypożyczał wielu narodom, sam zaś nie pożyczał.
Chizkuni
והלוית גוים רבים, “and you will lend to many nations;” to nations who were plagued with crop failures or storage problems in their barns.
Ibn Ezra
his treasury so called because its contents are dispensed only through His agency. Compare, “treasuries of the snow” [Job 38: 22]. Having previously mentioned “will grant you overabundance”, Scripture proceeds to mention rain, the lack of which is the primary cause of famine,
Or HaChaim
יפתח ה׳ לך את אוצרו הטוב, "G'd will open for you His store of goodness, etc." From this point on until the end of verse 13 the Torah describes the reward for fulfilling the positive commandments. This is why verse 13 concludes with the words "if you listen to the commandments of the Lord your G'd." The channels which G'd employs to direct the outpourings of His goodness to earth are activated through performance of commandments rather than through the passive refraining from violating negative commandments.