Who says "Amarti"?
Radak: The author.
Malbim: Straightness says so. It is planted in every person's nature, to love straightness and Tzedek. A Rasha who veers from this, he opposes his Nefesh's nature. His Nefesh afflicts him and pressures him to return to the good. Therefore, Resha'im are full of regret 1 .
Some cite this in the name of Chazal. The earliest source I found is Aristotle's Sefer ha'Midos, Sof 9:5. (PF)
Who are "Holelim"?
Rashi: They are Resha'im who confound Yisrael.
Radak: They are those who indulge in goods of this world and do not fear Elokim, for they think that they prospered due to their power.
What is the meaning of "Al Taholu"?
Radak: Do not engage in folly 1 .
What is the meaning of "Al Tarimu Keren"?
Radak: Do not raise your heads against Hashem, like you do, that you do not fear Him or humble yourselves in front of Him. He, and not Your power, benefits You!
