What event ultimately leads to the destruction of the church?

Mr. Brown's replacement is the Reverend James Smith, and he is not the tolerant and wise man that Mr. Brown was. Mr. Smith is fanatic and uncompromising, seeing the world entirely in terms of black and white. Under him, fanatics like Enoch flourish.

One night, the Mother of Spirits roams the villages, weeping for the death of her son. The spectacle is terrifying. Mr. Smith hears it, and for the first time feels fear. The egwugwu approach the church. They will not harm the people, but they could no longer allow the church to work its evil among the Igbo. They destroy the building.