Why does it say "Hen l'Riv u'Matzah"?
Radak: Your fast is only to quarrel. How will I desire it?!
Malbim: If you gather l'Shem Hashem, it is like a yoke on you. However, if you gather in order to quarrel, or in order "to hit with the fist of evil", then you desire it.
What is "Egrof"?
Radak: This is known in Chazal (the fist), like 'Ba'alei Egrofim' (Pesachim 53b).
Why does it say "Lo Satzumu cha'Yom"?
Rashi: [You do not fast] like the law of a [fast] day, to break (humble) your hearts, so that your voice will be heard above.
Radak: This is like keha'Yom. The prefix Chaf shows the truth of the matter, like "Hishav'ah Li ka'Yom" (Bereishis 25:33). You make heard above that you scream in Tefilah, as if you pour your Nefashos in front of Me, but it is not so. It is guile, as if I do not know your hearts.
Malbim: A fast to make your voice heard above is utterly unlike your fast for quarrels. The latter you do with desire, and the former is a burden on you.
