Why does it say "Ach"?
Rashi: Do so soon, so Tzadikim will praise Your name.
Radak: Tzadikim will praise Your name, but Resha'im will not.
Why does it mention Tzadikim thanking His name here?
Radak: When You do Mishpat against Resha'im, Tzadikim will praise and thank Your name.
What is the meaning of "Yeshvu Yesharim Es Panecha"?
Radak: They will constantly sit in front of You, to seek You and know Your ways.
Malbim: They are like those close to the king, who sit in front of him and see him himself. So they will grasp Your Elokus and grandeur itself, and Your Hashgachah Pratis.
Why does it switch from "Tzadikim" to "Yesharim"?
Malbim: "Yesharim" are at a higher level. They grasp You Yourself, and not only Your name.
