Adam Clarke

Beware of dogs - The Jews, who have here the same appellative which they formerly gave to the Gentiles: because the Gentiles were not included in the covenant, they called them Dogs; and themselves, the children of the Most High. Now, they are cast out of the covenant and the Gentiles taken in; therefore they are the dogs, and the Gentiles the children. Evil workers - Judaizing teachers, who endeavored to pervert the Gospel. The concision - Κατατομην· The cutting or excision; not περιτομην, the circumcision: the word is used by the apostle to degrade the pretensions which the Jews made to sanctity by the cutting in their flesh. Circumcision was an honorable thing, for it was a sign of the covenant; but as they now had rejected the new covenant, their circumcision was rendered uncircumcision, and is termed a cutting, by way of degradation.