Why was Okonkwo forbidden to beat his wife?

Beating is forbidden during the Week of Peace, as is all fighting and violence. There is a custom in this region to observe a week of neighborliness and good cheer before the sowing season begins.

When Okonkwo beats his wife, Ojiuigo, during the Week of Peace he is punished for "breaking the peace of Ani," the goddess of the village and the spirit that oversees the farming and its results. 

Okonkwo is reminded for the...

Beating is forbidden during the Week of Peace, as is all fighting and violence. There is a custom in this region to observe a week of neighborliness and good cheer before the sowing season begins.

When Okonkwo beats his wife, Ojiuigo, during the Week of Peace he is punished for "breaking the peace of Ani," the goddess of the village and the spirit that oversees the farming and its results. 

Okonkwo is reminded for the reason of his punishment when Ezeani comes to speak with him. 

"You are not a stranger in Umuofia. You know as well as I do that our forefathers ordained that before we plant any crops in the earth we should observe a week in which a man does not say a harsh word to his neighbor. We live in peace with our fellows to honor our great goddess of the earth without whose blessing our crops will not grow. You have committed a great evil."

Okonkwo is told to make a sacrifice to the goddess.

This episode demonstrates a few things about Okonkwo's character. He is short-tempered and feels that he must maintain strict control over his family life. He is afraid of appearing weak and so acts quickly and rashly. 

Violence is his first impulse and it springs from a fear that deep down he is weak like his father. In the killing of Ikemefuna, this violence erupts again. 

Yet, Okonkwo is repentant. He is willing to make the sacrifice to pay for his mistakes. Above all, Okonkwo desires the acceptance and respect of his peers. His behaviors are largely designed to keep well within the strictures of his culture and community, to show himself as a good man fulfilling his duties to his family and his village. 

Despite his best efforts, Okonkwo's lack of self-control puts him at odds with cultural norms from time to time, with drastic consequences. 

In beating his wife, Okonkwo allows his temper and his desire to avoid weakness overwhelm his sense of duty to the village.