In Things Fall Apart, sin is defined as a crime against the gods. Such transgressions occur when a member of society violates the most intimate bonds of family, especially with regards to one’s children or somehow insults an ancestral spirit. These sins call for quick and severe punishment, often including animal sacrifices, a heavy fine, various symbolic gestures of atonement, exile from one’s fatherland, or even death. Only when such payment is given can justice be served. If punishment is not doled out, not only is the sinner subject to divine wrath, but the entire community suffers.
Okonkwo sins when he murders Ikemefuna. The troubles that follow Okonkwo after the murder are a result of Okonkwo’s sin going unpunished.