I think what many of us tend to miss is that the ritual circumcision was the mark and symbol of coming under the Mosaic covenant, the distinguishing sign of Jew as opposed to Gentile, in a way that keeping kosher or wearing a yarmulkeh was not. It therefore gained a suignificance out of all proportion to its actual meaning in everyday life. This is why Paul and Luke are perpetually referencing circumcision as the key distinctive separating Jew from Gentile – it was the symbol par excellence of the Old Covenant which the New one they were preaching superseded.