What is "Kavod"?
Radak, Malbim: It is the Nefesh. "Afar will not tell Your Emes" (verse 10), but the Kavod (my Nefesh) will sing to You and thank You.
What is the meaning of "v'Lo Yidom"?
Radak: [Kavod, i.e. the Nefesh] will not be silent and cease [Malbim - to sing to You]
Why did he say "l'Olam Odeka"?
Radak: My entire life I will thank You for this, that You forgave me. I know that my honor will remain after [my death] and will forever sing to You.
Radak citing Shocher Tov: One who intended to do good, Hashem writes it as if he did it. David thought to build the Beis ha'Mikdash, and it says "Chanukas ha'Bayis l'David" (verse 1).
Malbim: Since You revived (cured) me for this purpose, my entire life I will thank You.