Circumcision was a major factor in Jewish identity. While the practice of circumcision itself is not unique to the Jews in the Ancient world, although some of the traditions based on the Hebrew Bible are specifically Jewish. Circumcision is given as a sign of the Covenant of Abraham in Genesis 17, yet the ritual itself did not confer “spiritual blessing” as a sign of the covenant. For this reason the prophets told the people that they needed a “circumcised heart – clearly a metaphorical use of the idea of circumcision (Deut. 10:16, 30:6; Jer 4:4; Ezek 44:7, 9).
There is strong evidence that during the intertestamental period and into the first century, at least part of the Jews thought that circumcision was required for the convert to Judaism. (See, for example, Schiffman in Jewish and Christian Self-Definition Volume 2 (Philadelphia: Fortress, 1981), 115-156, especially 125-127. Schiffman discusses Talmud Yebamot 46 and the importance of the Izates story in Josephus Antiq. 20.2.4, see this post for more details on this story).
For the Jew, circumcision was one of a handful of important boundary markers which set them apart from the rest of the world. For the Gentile, circumcision was a strange mutilation of the flesh. Greco-Roman writers who comment on Judaism usually ridicule the practice. Marital, for example, seems to find a great deal of (naughty) humor in the Jewish practice (Epigrams 7.35.3-4; 7,82, 11.94).
It is not the case that Paul’s rejection of circumcision for Gentile converts was motivated by practical missionary concerns. Paul did not consider circumcision such a road -block to Gentile mission that he rejected it so that his churches could reach the pagan world. As an analogy, the evangelical Christian church has more or less accepted rock-styled praise bands as necessary to appeal to the modern world. Most churches have (rightly) rejected the idea that worship music must be played only on a proper pipe-organ. In most cases , this shift in worship style is evangelistically motivated. Paul did more or less the same thing in rejecting the so-called strange elements of Judaism for his Gentile churches.
Such a view makes light of the practice of circumcision in the first century. If this is the sign of Abraham’s covenant given by God, how can it be rejected as inconsequential? Paul does not merely call circumcision for Gentiles meaningless, he says it is dangerous. If one allows himself to be circumcised, he is in danger of nullifying the grace of God! (See Gal 1:6-9, for example.) Paul arrives in Jerusalem in Acts 15 convinced that any Law added to the Gospel is no gospel at all, including circumcision. Whatever God is doing among the Gentiles in Asia Minor (Acts 14), there is no conversion to Judaism. Schnabel makes this point in Paul the Missionary in the context of the book of Galatians (126): “Paul insists that the Gentiles do not have to become Jews before they are accepted by God as followers of the Messiah” (emphasis added).