Although our salvation is secure, Paul alerts us to the possibility that we can be spoiled (Colossians 2:8), our faith can be shipwrecked (1 Timothy 1:19), and we can fall from our own "stedfastness" (2 Peter 3:17). These are not idle threats. There are those who are the "enemies of the cross of Christ" (Philippians 3:18), hence these startling descriptions in today's verse.
Dogs, both literally and metaphorically, are never mentioned in a positive context in Scripture. "Dogs" encircled the Lord Jesus while on the cross (Psalm 22:16). Blind watchmen are "dumb dogs" and ignorant shepherds are "greedy dogs," since neither are seeking the good of God's people (Isaiah 56:10-11). We are explicitly warned not to give "that which is holy unto the dogs" (Matthew 7:6). We must "beware of dogs" indeed.
Those motivated by evil come under severe condemnation. False prophets are called "wolves" (Matthew 7:15), false apostles are deceitful (2 Corinthians 11:13), and those who falsely profess Christ are abominable, disobedient, and reprobate (Titus 1:16).
The concision (mutilators) are those who demand the Old Testament circumcision as proof of conversion (Galatians 6:12-15), thus ignoring and nullifying the grace of God given through the Lord Jesus Christ.
All such workers of iniquity will be rejected by this same Lord Jesus when they insist that their works are sufficient for salvation (Matthew 7:22-23). HMM III