Rodney Stark, a sociologist who in the 1990s began applying the tools of his craft to the study of early Christianity, is always worth reading. Cities of God is an interesting, provocative, and often illuminating study of the spread of Christianity in the Roman Empire. It applies the methods of quantitative analysis to the geography, urbanism, and other aspects of the Christian movement and its major forerunners and competitors. Most of Stark's conclusions are neither new nor radical, but they are significant because they are supported by modes of analysis not typically employed by biblical scholars or historians of antiquity.
Among Stark's CONVINCING CONCLUSIONS:
(1) Christianity spread not through mass conversions but through the example and witness of rank-and-file believers who traveled for commercial and other reasons. (2) Sea travel was more important than Roman roads in facilitating the spread of Christianity and other eastern religions. (3) Christianity found especially fertile soil in large cities--especially port cities and Hellenized cities. (5) Cybele and Isis worship were important stepping stones--ritual, emotional, and intellectual--for many pagans who came to embrace Christianity. (5) Gnosticism (a dubious category) and Demiurgical religions were neither offshoots of Judaism nor early and widespread forms of Christianity but amalgams of paganism and Greek philosophy (especially Platonism) that had little appeal to most Greco-Romans, whether Christian or pagan. (6) Mithraism was never a serious competitor to Christianity but a male-dominated army cult with little appeal to the masses. (7) Constantine was not responsible for the triumph of Christianity. (8) It was the emperor Julian (the "Apostate") who exacerbated tensions between pagans and Christians. (9) Paganism did not end quickly but persisted into the fifth and sixth centuries.
Much less convincing--because they are not supported with much argument or evidence--are Stark's hypothesis cum theses concerning Judaism and the mission of Paul.
Among Stark's MOST DUBIOUS AND LEAST SUPPORTED CLAIMS:
(1) JUDAISM WAS A MISSIONARY RELIGION (pp. 6-7; etc). This claim is weakly supported by appeals to a few Old Testament verses and a statement of the Medieval Jewish philosopher Maimonides. It is not backed up by any evidence from Jewish sources of the Greco-Roman period and fails to consider the best scholarship on the subject (e.g., Martin Goodman 1994, Mission and Conversion; Shaye Cohen 1999, The Beginnings of Jewishness; Scott McKnight 1991, Light among the Gentiles: Jewish Missionary Activity in the Second Temple Period).
(2) PAUL DIRECTED MOST OF HIS MISSIONARY EFFORTS AT DIASPORA JEWS AND NOT GENTILES (pp. 120-139). This claim is belied by the testimony of Paul's own letters. It relies on an uncritical reading of the book of Acts. Paul certainly attended synagogues (see 2 Cor. 11:24) and no doubt evangelized Jews when he did (see 1 Cor. 9:19-21), but Gentiles were his first and primary target audience (e.g., Gal. 1:15-17; 2:7-9; Rom. 11:13). His letters simply to not reflect that he had spent the prior decade or two evangelizing Jews.
(3) PAUL DEMANDED THAT JEWISH CHRISTIANS CEASE OBSERVING THE LAW (pp. 130, 169). This claim is asserted without argument or appeal to evidence. It has no basis in either Paul's letters or even the book of Acts. Indeed, Acts suggests that did not make such demands of Jewish believers in Jesus (see Acts 21:20-26). Paul opposed forcing Gentile believers in Jesus to practice Torah, but no source tells us that he told Jewish believers to stop observing it. Paul regarded Torah observance as such as a matter of indifference (Gal. 5:5; 6:15; 1 Cor. 7:19). His view was that ritual Torah observance ("the works of the Law") does not make anyone, Jew or Gentile, members of God's covenant people or secure their final salvation (Galatians 3; Romans 3-4).
(4) JUDAIZING ACTIVITY IN THE 4TH AND 5TH CENTURY PROVES THAT SIGNIFICANT NUMBERS OF JEWS CONTINUTED TO CONVERT TO CHRISTIANITY INTO LATE ANTIQUITY (pp. 136-139). What Judaizing activity (following Jewish customs) more likely suggests is the reverse: Judaism (or at least aspects of Jewish observance) continued to attract Christians into late antiquity. Further, in patristic literature the label "Judaizing" often has nothing to do with following Jewish customs; in the writings of some church fathers, it is a polemical label for Christians whose Christology is too "low" or who interpret the Old Testament literally instead of figuratively (see, e.g., Shaye Cohen 1999, The Beginnings of Jewishness; Michelle Murray 2004, Playing a Jewish Game: Gentile Christian Judaizing in the First and Second Centuries C.E.).
(5) ANTI-JUDAISM SUGGESTS CLOSE PROXIMITY TO JUDAISM AND OPPOSITION TO IT (e.g., p. 169). This is not necessarily the case. Like the phenomenon of Judaizing, anti-Judaism need not imply direct contact with or influence from Jews or Judaism. As often as not, it looks like a matter of intra-Christian theological disputes and seems not have been encouraged by non-Christian Jews.
In sum, as a scholar of early Judaism and early Christianity, I find Stark mostly persuasive when he writes about early Christianity's relations to Greco-Roman paganism. But I find him wrongheaded in much of what he says about Judaism and Paul.