וּנְתָנָ֞ם יְהוָ֧ה אֱלֹהֶ֛יךָ לְפָנֶ֖יךָ וְהִכִּיתָ֑ם הַחֲרֵ֤ם תַּחֲרִים֙ אֹתָ֔ם לֹא־תִכְרֹ֥ת לָהֶ֛ם בְּרִ֖ית וְלֹ֥א תְחָנֵּֽם׃
and when the LORD thy God shall deliver them up before thee, and thou shalt smite them; then thou shalt utterly destroy them; thou shalt make no covenant with them, nor show mercy unto them;
Read kabbalistic (mystical) interpretation of Deuteronomy 7:2: and classical mystical sources.