Philippians 3:2-3 (ESV)
Look out for the dogs, look out for the evildoers, look out for those who mutilate the flesh. For we are the circumcision, who worship by the Spirit of God and glory in Christ Jesus and put no confidence in the flesh—
This seems like an odd thing to write to someone. But when you understand the context of Philippians and the early church is a powerful statement to write. There were those in the church who were teaching that you had to be circumcised along with faith in Jesus’ death, burial and resurrection. Paul calls them dogs, evildoers and those who mutilate the flesh. When writing to the churches in Galatia he actually called for them to be accursed:
Galatians 1:6-9
I am astonished that you are so quickly deserting him who called you in the grace of Christ and are turning to a different gospel— not that there is another one, but there are some who trouble you and want to distort the gospel of Christ. But even if we or an angel from heaven should preach to you a gospel contrary to the one we preached to you, let him be accursed. As we have said before, so now I say again: If anyone is preaching to you a gospel contrary to the one you received, let him be accursed.
To the church at Philippi he writes for them to look out for them. Staying away from sinners and evil does is part of God’s way. Note what this famous psalm states:
Psalms 1:1-2 (ESV)
Blessed is the man
who walks not in the counsel of the wicked,
nor stands in the way of sinners,
nor sits in the seat of scoffers;
but his delight is in the law of the LORD,
and on his law he meditates day and night.
We are to avoid those who avoid God.