לִ֤י נָקָם֙ וְשִׁלֵּ֔ם לְעֵ֖ת תָּמ֣וּט רַגְלָ֑ם כִּ֤י קָרוֹב֙ י֣וֹם אֵידָ֔ם וְחָ֖שׁ עֲתִדֹ֥ת לָֽמוֹ׃
Rache ist meine und Belohnung, gegen die Zeit, wenn ihr Fuß rutschen wird; Denn der Tag ihres Unglücks ist nahe, und die Dinge, die über sie kommen werden, werden sich beeilen.
Rashi on Deuteronomy
לי נקם ושלם means, with Me is prepared and held in readiness the punishment of vengeance, and it will recompense them according to their doings. As regards the word ושלם, it means that vengeance will pay them their recompense (וְשִׁלַּם is therefore a verb with the Vau conversive, the subject being the noun נקם which precedes it). — But some explain the word וְשִׁלַּם as a noun, having the same meaning as שִׁלּוּם “recompense”, when it would be of the same grammatical form as the noun in the phrase (Jeremiah 5:13) “And the דִּבֵּר is not in them”, where it has the meaning of דִּבּוּר, “Divine utterance”. And when will I recompense them?
Sforno on Deuteronomy
לי נקם, it is up to Me to do the avenging from My enemies.
Or HaChaim on Deuteronomy
לי נקם ושלם, "Mine is the vengeance and the retribution." As mentioned previously and in Avodah Zarah 3, when that day arrives G'd will remove the sun from its orbit and the wicked will be burned by it whereas the righteous will experience the sun's heat as therapy and be healed by it. The sequence of the words לי נקם ושלם, means that at one and the same time what will be G'd's vengeance against the wicked will be the payment of a reward for the righteous.