What do we learn from "ha'Lachof k'Agmon Rosho"?
Shabbos 54b: Gimon refers to bending.
Kidushin 62b: Agam means something that can be bent?
Rashi: The prefix Hei shows astonishment. Do I need you to bend your head like an Agmon?! Agmon is a bent needle used to trap fish (hook).
Radak: Agmon is a pit [in] which he bends his head. Hashem does not desire all these [external] deeds, rather, a broken heart, good deeds and Teshuvah from evil ways.
Malbim: Even if you would truly afflict yourselves, this would not be Hashem's desired fast. He does not desire Inuy, or even bending the head, wearing sackcloth and ashes. All the external deeds are only to arouse the hearts. They are the shells of the internal - the intents, which are the Ru'ach and Nefesh of these deeds. Without the intents, they are like dead bodies.
Why does it say "hala'Zeh Tikra Tzom"?
Rashi: The prefix Hei shows astonishment, therefore there is a Chataf Patach under it.
