This rather short monograph focuses primarily on Justin's Dialogue with Trypho, the Jew—Justin's attempt to argue the superiority of Christianity and to perhaps convert Trypho. Rokeai provides a detailed account of the literature related to the topic, and he discusses in full the Talmudic responses to some of the same issues that Justin discussed. His overall point, however, is that Justin is essentially Paul on steroids. He argues that Paul was essentially anti-Jewish as well and that his occasional positive comments about the Jewish religion were simply an attempt to soften his otherwise strong rhetoric against Jewish traditions and law. Justin, in turn, didn't try to whitewash was Paul was really saying.
I think that Rokeai is right to say that Justin took Paul's ideas and used them to create his anti-Jewish rhetoric, but I think he misreads Paul. I don't think he was against the Jewish law or traditions; I think he wore his Jewish heritage with pride and wasn't just putting on a show. Justin misread Paul, and Rokeai falls right in line with Justin's misreading.
Some interesting ideas about why Justin argued as he did. Who was his audience? Surely he wouldn't have found many Jewish fans, but the audience was probably mostly those who might have had a choice between Judaism and Christianity. Another interesting point: Justin had to tread down a narrow path. He was against Marcion, who was also anti-Jewish. But Marcion's conclusion was that the God of the Jews was an entirely different God and thus rejected the Old Testament. Justin didn't argue that, but he still had to find a way to critique the Jewish law, traditions, and writings. To do that he espoused not a different God but a God who had imposed law and traditions on the Jewish people because they were uniquely incapable of being good people. Failing with even that, God had found his true Israel in the Gentiles, who replaced the Jews and whose natural morality, or willingness to accept Jesus and thus obey the larger law of love, meant that they had replaced the Jews in God's heart. In this way, Justin could keep the Old Testament prophecies and symbolism but jettison its laws. This goes far beyond anything Paul espoused. Paul noted the Jewish inability to obey God, for sure, but he didn't ground it in an idea that somehow non-Jewish people could do better, and especially not without the guidance laid out in the Old Testament; rather, he noted that because no one could follow the law, faith only in Christ could save, because all are otherwise due for the penalty of breaking that law: death. But as he notes, that doesn't then mean the law is bad or that it no longer applies; rather, believers were to live accordingly thereafter. Jewish people, not seeing Christ, meant that they were still under the penalty, but Paul noted that one day they would be shown the way accordingly and be welcomed back into God's fold. Non-Jewish people who took on the faith and lived accordingly certainly did become Israel, but they didn't replace the old Israel: they were welcomed into it.
