On his webiste Pullman writes about the theme of the new book:: 

"I've always been fascinated by the two parts of the name of Jesus Christ, and by the difference between them. Another thing that's interested me for a long time is the way in which the Christian church began to formulate its beliefs and establish a canon of scripture: there were many more gospels than four, but why were those four chosen and others left out? When did Paul begin to write his epistles? Was what he said different from what the gospels say? Do the gospels even agree with one another? Was there a difference between Jesus and Christ? My version of the Jesus story doesn't attempt to solve these questions, but I hope readers will find it interesting."