Many of Achebe's novels focus on the disparity of understanding that exists between the cultures of the native Africans and the culture of Europe. Colonization run amuck in Africa has had devastating effects because the two cultures see the world differently. Europeans have long been influenced by a Judeo-Christian view of the world, heavily influenced by the changing technology of the day. African culture has been influenced by a polygamous view of the world, influenced more by tribal and family relationships.
The Trinity represents both this disparity of understanding and the illogical behavior of Europeans. The Trinity is the most illogical tenet of Christian belief - that God has a son, but no "wife", and that a holy spirit exists separate from both these divine individuals. Christians pray separately to God and to Jesus. For a culture that has always lived with clear hierarchy, and a need to understand who is in charge, this "tri-focal" power is baffling. Symbolically, the Europeans have also come to Africa to colonize, to take control, but they also behave as if they want to "live in harmony" with the Africans. Baffling, and contradictory. The tribal people, even those who accept the new faith, can not reconcile the the confusing nature of the Trinity.