We learn that the fine flour should be composed of both the right and left side.
[Verse 657] Moses explains the flour by talking about Isaac, the left hand of Zeir Anpin, and Abraham, the right hand of Zeir Anpin. He says the fine flour is the lower Shechinah, as it has no connotation of darkness. Just as the chaff and straw have to be removed from the grain during threshing, Yisrael must remove any dark ones that become intermingled with them. Moses says that darkness is the Evil Inclination.