1)
How does this answer why David does not answer them?
1.
Radak: Why should I argue with them? I have no benefit from them. I hope only to You!
2.
Malbim: I relied on Hashem to answer me (save me from them).
2)
How will Hashem answer him?
1.
Rashi: He will redeem and save Yisrael from those who revile them.
2.
Radak: You are Master over all, and my G-d to execute my Mishpat against the Resha'im.
3.
Malbim: You will save me from them.
