Why does it say "Ga'arta Zedim"?
Radak: Past tense used in place of future (this is common in Nevu'ah). When Ga'arah is not followed by the prefix [or a pronoun beginning with] Beis, it is an expression of destruction and curse. Destroy the cursed intentional sinners, who forget Your Mitzvos.
Malbim: This addresses [not reaching perfection due to seeing] Resha'im succeed and Tzadikim are disgraced and lowly. It says that You always rebuke the cursed Zedim (those who are brazen to intentionally argue with Emunah and Toras Hashem) with punishments.
Why does it say "Zedim" and "Shogim"?
Radak: They intentionally neglect learning, and err about Mitzvos, because they do not know 1 . I always desire Mitzvos and Mishpatim, and they do not; they engage in follies of the world, or sit in corners, and do not desire to learn.
Malbim: Shegagah is in investigation - "v'Chi Sishgu v'Lo Sa'asu Es Kol ha'Mitzvos ha'Eleh" (Bamidbar 15:22) refer to a ruling [permitting] to serve idolatry. Via this, they err about all the Mitzvos, for idolatry is equal to all the Mitzvos.
Avos 4:13: Be careful about learning, for a mistake in learning is considered Mezid. Radak - this is because he intentionally neglected learning.
Why does it say "mi'Mitzvosecha"?
Radak: Through their Shegagah, they leave the Mitzvos. Therefore, it does not say b'Mitzvosecha.
