Ehrman discusses the origins of Christian writings, the low literacy rates in the ancient world, and how early texts were likely read aloud in congregations. A central theme is how scribes introduced numerous changes, sometimes unintentionally and sometimes deliberately for theological or apologetic reasons, as evidenced by variant readings concerning Jesus's emotions or divinity.

The book outlines the shift from amateur scribes in the early centuries to professional Christian scriptoria in later periods, which improved copying accuracy, and details the ongoing academic quest to reconstruct the original words of the New Testament authors.