Paul, whose epistles instructed small Christian communities in the Near East on points of behavior and doctrine, was writing at a time when Christianity was still primarily a Jewish movement. In his desire to emphasize the newness of his faith, and the rupture with Judaism that Jesus Christ represented, he cast the two religions as a series of oppositions. Where Jews read scripture according to the “letter,” the literal meaning, Christians read it according to the “spirit,” as an allegory predicting the coming of Christ. Likewise, where Jews obeyed traditional laws, Christians were liberated from them by faith in Christ—which explained why Gentile converts to Christianity did not need to follow Jewish practices like circumcision. To “Judaize,” to use a word Paul coined, meant to be a prisoner of this world, to believe in the visible rather than the invisible, the superficial appearance rather than the true meaning, law rather than love. More than a theological error, Judaism was an error in perception and cognition, a fundamentally wrong way of being in the world.
The problem, as Nirenberg argues in the richest sections of his book, is that this is an error to which Christians themselves are highly prone. Paul and the early Christians lived in the expectation of the imminent end of the world, the return of Christ, and the establishment of the new Jerusalem. As the end kept on not coming, it became necessary to construct a Christian way of living in this world. But this meant that Christians would have need of law and letter, too, that they would need to “Judaize” to some degree.