Look out for the dogs, look out for the evildoers, look out for those who mutilate the flesh. (ESV)
The entire letter to the Philippians has a continual theme. Joy. Joy is only found in the Lord. Even though Paul is writing this letter from a prison cell, he remains joyful because joy is something that is constant in the Lord regardless of our circumstances. In the previous verse Paul reminds the Philippians again to "rejoice in the Lord."
This admonition to rejoice is now followed with a warning. Paul says, "Look out!" There are joy-killers on the loose. They want to rob you of your joy and place unnecessary burdens on you and destroy the freedom you have in Christ, who is your joy. Isn't it always the case that where someone is experiencing joy someone else wants to be the party pooper.
Paul uses three descriptions of these joy-killers. Each description is talking about the same group of party poopers. Who are they? Judaizers. Judaizers were Jews who insisted that the Gentiles at Philippi were not truly saved because they had not been circumcised. These legalistic Jews could not accept that salvation was an act of grace not by any works of men, including circumcision.
There is some irony in the words Paul uses here. The Jews loved to call Gentiles dogs. Here Paul throws the insult back on the Jews. Paul calls the Judaizers evildoers, even though they would claim true legalistic righteousness. And he describes their circumcision as mutilation, rather than a careful cutting in a proper ceremony unto the Lord. The bottom line is the heart of the Judaizers was completely wrong and their physical works were irrelevant.
Do you know any kill-joys? Party poopers? If you belong to Jesus Christ you should walk in the joy of the Lord. Do not listen to party poopers. And for God's sake, don't be one!