Obierika, a man of the clan?

Obierika, apart from Umuofia

In the beginning of Things Fall Apart, we meet a member of the Umuofia tribe, Obierika. He is a friend of Okonkwo and a father. But is Obierika a true character as a friend to Okonkwo? For three years, Okonkwo housed a boy from a neighboring clan named Ikemefuma. The Oracles of the Hills has declared that Umoufia must kill the boy. All of the clan's elder members, including Okonkwo, go out to fulfill the calling of the gods. Surprisingly, Obierika does not go. Okonkwo asks him why he questions the authority of the gods and Obierika responds, " ' I do not. Why should I? But the Oracle did not ask me to carry out its decision' " (Achebe 66). This shows that Obierika has a sense of insecurity of his clan's practices and beliefs. In chapter 13, Okonkwo commits a female crime and must leave for seven years. As a calling of the earth goddess, she sends the men of the clan to go to Okonkwo's house and destroy everything that is there. Obierika was one of them. This does not seem to me that Obierika is a real friend to Okonkwo or true to his beliefs. What could have possibly caused Obierika to join in on the destruction of his friend's home? Is there any connection to the last sentence in Chapter 13, "As the elders said, if one finger brings oil it soils the others" (Achebe 125)?