Somewhere, scattered throughout the blog, are posts on Philippians up though 3:16. I'll gather them all together when I'm done as I have with 1 Thessalonians and Galatians.
3:17 Become fellow imitators of me, brothers, and be watching those who walk thus, just as you have us as a model.
It is jarring to some popular conceptions of Paul to hear the confidence he had in putting himself forward as an example of how to live. Not only does good exegesis undermine the idea that Romans 7 gives Paul's ongoing struggle with Sin. Verses such as this one show definitively that Paul considered his own pattern of life a model for his churches to emulate. "Do as I do" invites a striking examination of his own "walking" in the world.
3:18-19 for many walk with regard to whom I used to say often to you--and now I also am saying, crying--[they walk as] enemies of the cross of the Christ, whose end is destruction, whose God is the belly and [whose] glory [is] in their shame, who think earthly things.
The referent of these verses is somewhat obscure. Does Paul refer to 1) Gentile opponents to the Christ movement, 2) non-believing Jews who oppose faith in Christ, or 3) Christian Jews who disagree with Paul's way of thinking? The following verse implies that such individuals prize in some way "citizenship" on earth. This could refer to Roman citizenship or citizenship in a particular city, which would make sense given that Philippi was a Roman colony whose citizens were automatically citizens of Rome. But it might also be a dig at Jews, Christian or otherwise, who Paul sarcastically implies are too attached to the earthy Jerusalem.
On the one hand, it is easier to see Paul "crying" in relation to his own brothers in Israel than about Romans, per se (cf. Rom. 9:2-5), unless we mean to say he cries over his own difficulties. But this latter thoughts seems less likely. The mention of the "cross" of Christ reminds us of Paul's accusations of other Christians who argue over keeping the Jewish Law. Paul considers such believers to "boast in flesh" (Gal. 6:13) and want a "good showing in flesh (6:12). They do not want to be persecuted for the "cross of Christ" (6:12).
In our dating of Galatians and Philippians, Paul writes Galatians just after 1 Corinthians and only a year or two before Philippians, all while ministering in and around Ephesus. The conglomeration of themes thus would relate to considers he had particularly in this period. The fact that Philippians 3 begins with reference to the "mutilators," which we take as Christian Jews who insist on circumcision and full conversion to Judaism, it is reasonable to think at the end of the chapter that he is closing the page on this discussion.
Paul thus reasonably has Jews, Christian or otherwise, who oppose the Christ movement as he once did as a corruption of Jewish faith. The reference to the belly is opaque. Is it too far of a stretch to think of things like circumcision as part of the realm of the "belly"? Certainly it could be an allusion to food laws and table fellowship, an issue that caused significant conflict for Paul at Antioch (cf. Gal. 2).
Those Jews who glory in such "works of Law," elements of Jewish separation and distinction, were in fact glorying in things that were to their shame, in Paul's view. These individuals were rather headed for destruction, by which Paul may be thinking the judgment that will come to the living who are not in Christ when he returns to judge the world. Such individuals are thinking "earthly" rather than heavenly, or as Paul puts it in Galatians, they are enslaved to the elements of the world (e.g., Gal. 4:3, 9).
3:20 For our citizenship is in the heavens, from which also we await a Savior, the Lord Jesus Christ,
If this line of thinking is correct, then Paul is contrasting citizenship in the heavens with those who overly prize the earthly Jerusalem. Again, we find in Galatians a similar theme as Paul contrasts the heavenly and the earthly Jerusalem (Gal. 4:25-26). At the same time, the imagery of citizenship would have been readily understood by the Philippians, for the city of Philippi was a Roman colony. Roman colonies had the highest status of any cities in the Roman world. Their citizens were automatically citizens of Rome, although not everyone that lived in a city was considered a city of it. The official language of the city was Latin, even though Paul easily can write to them in Greek.
The model of living in a city at somewhat remove from the place of citizenship is apt here. Roman citizens might not live in Rome and yet have citizenship based there. In another way, Jews might in a sense be citizens of Jerusalem, even though they live in the Diaspora. So believers are citizens of heaven, even though they are located on earth.
The notion of a Savior coming from the place of citizenship might also easily have Roman overtones. The Roman emperor Augustus, for example, was fashioned as the Savior of the Roman world. Whether Paul's eschatology has undergone any modifications in Philippians or not, he still expects Christ to return to earth at some point bringing salvation to those who believe and destruction to those who do not.
The question of whether Paul also implies that we will at some point go to our "home city" in heaven is a matter of some debate. Some scholars would argue quite strongly that Paul does not in any way picture believers "going to heaven" in some way. However, it is hard to imagine what it might mean to die and go to be with Christ (Phil. 1:23-24) if it does not picture going to heaven in some way, at least in the time prior to the resurrection, assuming Paul still has a conventional understanding of resurrection as something that takes place at some point in the future rather than at death.
3:21 ... who will transform the body of our humility into the same form as the body of his glory according to the working that makes him able even to subject all things to himself.
The time that Paul has in mind is apparently the point when Christ as Savior returns from heaven in salvation and destruction. The verse thus speaks directly of the transformation that will happen to the earthy bodies of those believers who are alive at the point of Christ's arrival or parousia. This is the sort of transformation Paul discusses in 1 Corinthians 15 that there will happen to the dead in Christ. Whether 2 Corinthians 5 implies Paul developed to come to see this transformation taking place at death is a matter of debate.
Our current earthly bodies are thus "bodies of humility" or perhaps even humilation, thus reinforcing the sense that it is foolish to focus on matters of the "belly" or the foreskin. The verse also implies that the glorified body of believers will be the same as the glorified body that Christ received at the point of his resurrection. It is in this glorified state that Christ will eventually see everything subjected to him (e.g., 1 Cor. 15:25-28).