First, Reza Aslan is not a New Testament scholar. In Zealot, he is writing well outside his own academic training. This does not mean that his book is a bad one, or that he shouldn’t have written it, only that it is primarily a sifting and re-presenting of the work of actual NT scholars.
Moreover, there is nothing remotely new in Aslan’s book. Its general outlines very closely follow the story told by John Dominic Crossan in his 1994 book Jesus: A Revolutionary Biography , which was itself a kind of summation of work Crossan and his colleagues had been doing for the previous quarter-century. (Aslan is more prone to see Jesus as a consciously political revolutionary than Crossan, who writes of Jesus’s message, “It did not invite a political revolution but envisaged a social one at imagination’s most dangerous depths” ; but in other respects Aslan’s picture of Jesus so closely resembles Crossan’s that it’s peculiar, at least, to see the earlier book go barely acknowledged in those notes.) Aslan makes no new discoveries, and makes no arguments that haven’t already been made — in some cases very long ago.
Let’s look at just one issue that tells us something about how Aslan handles his business. In Chapter 4 he writes,
Whatever languages Jesus may have spoken, there is no reason to believe that he could read or write in any of them, not even Aramaic. Luke’s account[s of Jesus’s literacy] … are both fabulous concoctions of the evangelist’s own devising. Jesus would not have had access to the kind of formal education necessary to make Luke’s account even remotely credible.
This an exceptionally definitive statement in two noteworthy ways.
First, Aslan asserts that Luke was a conscious fabulist. Yet even if Luke were wrong about Jesus’s literacy — or about anything else — there is more than one way to explain those errors. For instance, Richard Bauckham’s important and much-celebrated book Jesus and the Eyewitnesses  — which Aslan appears not to know — makes a strong case that Luke’s Gospel, like the others, is based on the testimony of those who claimed to be eyewitnesses. Especially since Luke places such emphasis on his attempt to gather reliable witnesses to the life of Jesus, wouldn’t it make sense to attribute his errors (if they exist) to his interviewees’ lively imaginations or poor memories, and to his own credulousness, rather than to intentional deception? Yet Aslan never considers any other possible explanation than the one he blandly asserts without argument.
But, second, can we be so sure that Luke was wrong about Jesus being literate? Aslan again just states that Jesus could neither read nor write, but if we look at the bibliographical essays at the end of Zealot we discover that he knows perfectly well that the situation is far more complicated than that. One of the chief sources he cites is John P. Meier’s Jesus: A Marginal Jew , and, as Aslan must acknowledge, “Meier actually believes that Jesus was not illiterate and that he even may have had some kind of formal education, though he provides an enlightening account of the debate on both sides of the argument” (230n). So there’s an argument on this point? One wouldn’t learn that from reading the actual text of Zealot, only from burrowing deep into the apparatus.
In fact, Aslan is following the logic of Crossan here, who wrote — though again Aslan does not cite him —, “Since between 95 and 97 percent of the Jewish state was illiterate at the time of Jesus, it must be presumed that Jesus also was illiterate” (Jesus: A Revolutionary Biography 25). Aslan, as one might expect, just says “97%” — but both he and Crossan are wildly oversimplifying an immensely complex question, as I discovered when I tried to navigate the vast pile of evidence provided by Catherine Hezser in her Jewish Literacy in Roman Palestine . Confession: I didn’t get far in Hezser’s book, but far enough to realize that the invocation of statistics like “between 95 and 97 percent” and “97%” is a comically inept attempt to use numbers plucked from the air to give a false appearance of scientific accuracy in overwhelmingly difficult and evidence-poor situations.
The chief point I want to make here is that in claiming that Jesus was illiterate Aslan is (a) asserting flatly a point that is seriously disputed among New Testament scholars and (b) making no new claim. Indeed, the claim was not remotely new when Crossan made it: probably armchair atheists have been making it since before there were armchairs, but among New Testament scholars it goes back at least to Light from the East by Adolf Deissmann , the first edition of which appeared in 1908.
So, in sum: Reza Aslan’s book is an educated amateur’s summary and synthesis of a particularly skeptical but quite long-established line of New Testament scholarship, presented to us as simple fact. If you like that kind of thing, Zealot will be the kind of thing you like.