Joshua, as his name suggests, is the character who represents African openness and welcome towards Christianity and unbridled support for the way that Christianity has usurped tribal religion, beliefs and practices. This is shown by the massive conflict caused by Muthoni's decision to go through the circumcision ritual so that she can feel accepted as a women in the Gikuyu culture. As a Christian, Joshua has forbidden his daughters to become circumcised, which he sees as being against Christianity. Note what Muthoni and her sister, Nyambura, say to each other as they discuss Muthoni's idea:
You and I are now wise in the ways of the white people. Father has been teaching us what he learnt from the missionaries at Siriana. And you know, the missionaries do not like the circumcision of girls. Father has been saying so. Besides, Jesus told us it was wrong and sinful.
In Joshua therefore we can see the way that the novel uses him to represent one view of white people and Christianity: that of enthusiastic acceptance and displacement of traditional religion and beliefs. This of course leads to the central conflict in the novel as different characters with different opinions of the whites and Christianity are brought into conflict with each other.