While I can't help but see the parallels between the Ibo & Christian religion and that the only real difference preached here is that of "just don't murder people", this passage does wrap up quite well some of the "cracks" in Ibo culture, why the missionaries were so successful.
The interpreter/missionary responds to why the Christian religion's God is better simply with a variation of "he doesn't tell you to kill your friends or family". Both of these are practiced by the Ibo culture, as seen with the ruthless murder of Ikemefuna, and with the murder of twin children.
Looking at Nwoye, to whom Ikemefuna was like a brother to, it is immediately obvious why this religion is more appealing, as the cracks are much more evident in his life. For those in the culture for whom the cracks are not as evident, such as the higher up class members, this takes longer.