Why does it say "u'Kchu Kemach" with the prefix Vov?
Radak #1: Sometimes the prefix Vov appears at the beginning of a matter, and it is not connected to the previous matter, e.g. "va'Yisa Avraham Es Einav" (Bereishis 22:4) and similar verses.
Radak #2: It hints to a word that was omitted, i.e. Lechu u'Kchu (go and take).
Why did he say to put flour? It should suffice to cure the effect of the Paku'os! And why didn't he cure the damager with another damager, like he cured the bad water of Yericho via salt (2:21)?
Malbim: The poison transformed the food from something that sustains the body to something that destroys it, even after the poison itself was removed. Miracles do not create from nothing, rather, from something, so he needed something that sustains. A small amount of flour transformed the entire food into something that sustains.
How will it help to put flour in the pot? They already poured [into bowls]!
Radak: He commanded to return from the bowls to the pot before casting in the flour, lest he need to add flour to every bowl.
Did he do anything to cure those who already ate?
Malbim: "V'Lo Hayah Davar Ra ba'Sir" - this was retroactive (it was as if they never ate poison).
