NOTE: This is a condensed excerpt from my forthcoming (2014) commentary on Philippians.
Who then are these preachers with less than commendable motives? First, since Paul is describing his own circumstances, he is almost certainly referring to preachers who are active in Rome where he is in custody. Second, the fact that they preach Christ indicates that they are not the same people mentioned in 1:27-30, 3:2, or 3:18-21. In each of those passages the actions of these groups are described as antithetical to the gospel message itself, whereas here the message is correct while the motives for preaching it are not. Third, about five years before writing this letter Paul had written the Roman church in part to address disagreements over observing food laws and elements of the Jewish calendar (Romans 14:1–15:13). Although we do not know how the letter was received by those in Rome, it is certainly possible that Paul’s attempt to bring unity may not have succeeded. This, along with various rumors of Paul’s rejection of the Mosaic Law, may have been enough to prompt some Roman Christians to preach the gospel in an effort to diminish Paul’s influence and thus cause him trouble. Some thirty years later, Clement of Rome wrote that “Because of envy and jealousy [phthonon; cp. Phil 1:15], the greatest and most righteous pillars were persecuted and fought to the death … Because of jealousy and strife [erin; cp. Phil 1:15] Paul showed the way to the prize for patient endurance” (1 Clement 5:2, 5).
Regardless of who these preachers are, Paul likely mentions them not merely to explain his own circumstances but because of potentially similar issues in Philippi. Throughout the letter Paul addresses the importance of unity, not looking out for one’s own interests, and prioritizing the gospel above personal preferences. Thus Paul’s own example anticipates his exhortations later (1:27–2:18; 4:1-9) in the letter and prepare the way for the ultimate example of self-denial, Jesus Christ (2:5-11).
Paul demonstrates a tenacious commitment to the progress of the gospel regardless of the implications for him. His attitude reflects that his ministry is not about him, but rather centers on the one he preaches. As Paul testifies elsewhere, “what we preach is not ourselves, but Jesus Christ as Lord, with ourselves as servants for Jesus’ sake” (2 Cor 4:5). Yet sadly “The robe of ‘Christian ministry’ cloaks many a shameless idolatry.” The focus of a gospel ministry should not be the personality of the one preaching, but the person who is preached—Jesus Christ.
 For a detailed listing of the various suggestions, see Reumann, Philippians, 202-07.
 The fact that Paul describes them as preaching Christ makes it clear that these preachers are not false teachers such as those he corrects in Galatians and 1-2 Corinthians. Thus it is not so much that Paul has mellowed in his older years (as suggested by some such as Bockmuehl, Philippians, 81), but rather that Paul is dealing with very different circumstances.
 Along similar lines see Fee, Philippians, 121-23; Bockmuehl, Philippians, 77-78; Silva, Philippians, 64-65; Witherington, Philippians, 81-82.
 Bockmuehl, Philippians, 80.