In Phil. 3:2 Paul uses the deliberately offensive wordkatatomē, ‘those who mutilate the flesh’ (RSV), ‘the concision’ (AV). He is not defaming circumcision on Christians (cf. Gal. 5:12). The cognate verb (katatemnō) is used (Lev. 21:5, LXX) of forbidden heathen mutilations. To Christians, who are ‘the circumcision’ (Phil. 3:3), the enforcement of the outmoded sign is tantamount to a heathenish gashing of the body.
Motyer, J. A. “Circumcision.” Ed. D. R. W. Wood et al. New Bible dictionary 1996 : 205. Print.