The NIV's whatever happens translates the adverb "only," a word "lifted like a warning finger" (Barth 1962:45) to catch their attention about present realities. Paul expects to be released from his present imprisonment partly for the sake of his Philippian brothers and sisters' further "progress and joy" regarding "the faith." But in the meantime, while Paul is still "absent" from them, he wishes to hear the same kind of good report "about your affairs" (NIV about you) that he would hope to find had he been able to come now with Epaphroditus.
At issue is how the Philippians conduct themselves, meaning live out the gospel in Philippi. Pivotal to the present appeal is that instead of the ordinary Jewish metaphor "to walk [in the ways of the Lord]," Paul uses a political metaphor, which will appear again in 3:20-21. The people of Philippi took due pride in their having been made a Roman colony by Caesar Augustus, which brought the privileges and prestige of Roman citizenship. Paul now urges them to live out their citizenship (conduct yourselves) in a manner—and the sentence begins with these emphatic words—worthy of the gospel of Christ. What is intended by this wordplay is something like "Live in the Roman colony of Philippi as worthy citizens of your heavenly homeland." That, after all, is precisely the contrast made in 3:17-20, where "our citizenship is in heaven," in contrast to those whose minds are set on "earthly things."
The use of this metaphor is a brilliant stroke. Not only does it appeal to their own historic pride as Philippians, but now applied to their present setting, it urges concern both for the mission of the gospel in Philippi and especially for the welfare of the state, meaning in this case that they take seriously their "civic" responsibilities within the believing community. Their being of one mind and heart is at stake; disharmony will lead to their collective ruin.How are they to bring this off? By standing firm in the one Spirit as they contend side by side as one person for the faith of the gospel. With these words, and in typical fashion, Paul switches metaphors, this time to an athletic contest, probably used metaphorically in turn to suggest a battle. The image is of people engaged in spiritual warfare (imagery that will hardly be lost on those who live in a military colony!), standing their ground firmly by the power of the Holy Spirit, who as the one Spirit is also the source of their unity (cf. 1 Cor 12:13), thus anticipating 2:1. Despite the frequency of its appearance in English translations, this phrase can scarcely mean in one spirit (NIV), as though it meant to have a common mind about something. Such an idiom with the word spirit is unknown in all of Greek literature. Paul himself uses this phrase elsewhere to refer to the Holy Spirit (1 Cor 12:9, 13; Eph 2:18), precisely in places, as here, where Christian unity is at stake.
They are urged thus to stand firm in/by the one Spirit so as to contend together as one person for the faith of the gospel. Here we are at the heart of things: their need to have harmony within the Christian community as they live out the gospel in Philippi. The gospel is the beginning and end of everything for Paul. Thus for them to live out their (heavenly) citizenship in a manner worthy of the gospel means for them to contend for the faith of the gospel, and to do so in the unity that only the Spirit brings. All the more so now because they are facing some kind of opposition that is resulting in suffering.