Part 1 was so engrossing, and as an ex Catholic myself albeit one still interested in early Christian history, I thought Carrère captured the feelings of struggling with faith and belief and lapsing back into atheisism perfectly well. Part 1 is reflective and I could not put it down. 

Part 2 goes into the historical fiction of the life of Paul and Luke and this is where he lost me. Carrère presents facts mixed with his own speculation, often without differentiation, often just plain wrong. He info dumps on the reader, probably correctly assuming the average reader would not know the history of the early Christians, which is fair enough except he speculates on things, presents such speculations in the same breath as historical facts. If I wanted to spend time reading about the lives of the early Christians why would I not just spend it reading from actual historians specializing in that time, rather than listen to a journalist / screen writer?