Why does it mention judging cases of Aniyim?
Malbim: Do not think that he interrupted his meal only for great matters. He interrupted even to judge Oni and Evyon 1 .
I.e. both litigants are poor. Surely the claim is for a small amount!
Why does it say "Az Tov"?
Malbim: He was not happy due to eating, rather, for judging the oppressed.
What is the meaning of "ha'Lo Hi ha'Da'as Osi"?
Refer to 9:23:3:1-4.
Radak citing Targum Yonasan: [Knowing Me] is knowing My desire.
Sha'arei Teshuvah 4:5: Making the truth known, and returning it to its eminence is honor of Hashem.
Malbim: [Doing Mishpat and Tzedakah] is testimony that he knows Me - "Lo l'Adam Tishpetu Ki la'Shem v'Imachem bi'Dvar ha'Mishpat" (Divrei ha'Yamim II, 19:6). How did you do the opposite, to steal the wage of Aniyim?!