Why did he say "va'Hakimeni"?
Radak: This is opposite what they say, that I will not rise.
Malbim: Even though before (verse 5), he despaired from life, after he saw the clamor of his enemies, he began to ask to recover, in order to pay them. Since they rejoiced over me, You must raise me - "bi'Nfol Oyvecha Al Tismach
What will he pay them?
Radak #1: It is for the evil that they said about me when I was ill. He did not say that he will do evil to them, for he said "va'Achaltzah Tzorerai Reikam" (7:5)! Rather, the 'payment' will be to inform them that it was evil for them to plot against him when he was ill.
Radak #2: The 'payment' will be that David will not wear sackcloth when they are ill, not pray for them, and not be pained over their pain (like he used to do).
Radak citing Rav Sadya Gaon: I will pay to them good in place of evil, like was David's practice - "va'Ani ba'Chalosam Levushi Sak
