וְהָיָה֩ כִֽי־יָבֹ֨אוּ עָלֶ֜יךָ כָּל־הַדְּבָרִ֣ים הָאֵ֗לֶּה הַבְּרָכָה֙ וְהַקְּלָלָ֔ה אֲשֶׁ֥ר נָתַ֖תִּי לְפָנֶ֑יךָ וַהֲשֵׁבֹתָ֙ אֶל־לְבָבֶ֔ךָ בְּכָל־הַגּוֹיִ֔ם אֲשֶׁ֧ר הִדִּיחֲךָ֛ יְהוָ֥ה אֱלֹהֶ֖יךָ שָֽׁמָּה׃
And it shall come to pass, when all these things are come upon thee, the blessing and the curse, which I have set before thee, and thou shalt bethink thyself among all the nations, whither the LORD thy God hath driven thee,
Read halakhic rulings (Jewish law) on Deuteronomy 30:1: and classical halakhic sources.