What do we learn from "Baz l'Re'ehu Chotei"?
R. Yonah: An Ashir should not disgrace an Oni, even if he has the upper hand over him, for many love the Ashir, and even the poor hate the Oni 1 . Also Iyov said "Im Hanifosi Al Yasom Yadi" (31:21). Re'ehu is like "Lo Sa'ashok Es Re'echa" (Vayikra 19:13), "v'Chol Asher l'Re'echa" (Shemos 20:14). All Yisrael are called Re'im 2 . Disgrace of colleagues is a sin, but honor and giving grace are obligatory only for the humble and Yir'ei Shamayim.
Malbim: The laws of Chachmah require one to love humility and lowliness, give grace to the humble and hate haughtiness. This one hates the Oni because he is poor and downtrodden - this is the opposite! It is a Chet against the laws of Chachmah.
Why is "Mechonen Anavim Ashrav"?
R. Yonah: Chonen is the simple conjugation - grace and compassion. Mechonen is a four-letter root; he causes them to have grace in his eyes. This is like "v'Es Afarah Yechonenu" (Tehilim 102:15) - its earth has grace in his eyes, like "Ratzu Avadecha Es Avaneha" (ibid). He does not disgrace him due to his poverty, for he recognizes his attribute of humility. Anavim is written like Aniyim. Shlomo said this 1 only about three Midos. Most people, when they see good attributes, e.g. fear of sin and Chasidus in an Oni, even though they believe that these attributes are greater than wealth and honor, when they see an Oni disgraced in people's eyes and he does not succeed, they do not honor him, and he does not have grace in their eyes. They say that his patience is his lowliness, due to his poverty. One who drew his desire to Yir'as Hashem and Avodas Hashem, and elevated his desire over nature, he recognizes the attribute of humility and every good Midah [even] in an Oni. [Even] if the Oni is disgraced in people's eyes, [elevated people] give grace to attributes, and not to successes of worldly follies. David said "Chaver Ani l'Chol Asher Yir'ucha" (Tehilim 119:63).
Malbim: He has happiness of the Nefesh. He learns love of humility and hatred of pride.
Magihah: Ashrei.