Why does it say "Ki"?
Rashi: Because You do not desire evil, it is proper that You [judge Yisrael's enemies, and] eradicate Resha'im from the world.
Radak: I look forward to You (Your salvation) because You do not desire Resha'im; if so, You desire me, and not my enemies.
Malbim: The nations who served idolatry attributed to their gods deceit and all bad Midos. They attributed every force found in nature, to a supreme power from which the influence comes. This is for good, and also for bad, e.g. cruelty, pride, envy, and vengeance. A god who desires good will fear a god who desires evil, for sometimes it defeats it, like is known from the follies of Greek (mythology) and their songs. Hashem, even though all powers come from Him, He does not desire evil. Refer to 5:5:2:3.
What is the meaning of "Lo Yegurcha Ra"?
Rashi: Evil will not dwell by You.
Radak: It will not dwell by You. Also "Gedelani ch'Av" (Iyov 31:18) is to grow up with me; many verses are like this. Ra is an evil man, or a noun (evil), like Resha mentioned (earlier in this verse).
Malbim: You are unlike even the nations' gods that desire good, for they fear evil. You, evil does not dwell by You, and You do not fear it. You are the source of good and Chesed. Evil is separate from You.
