Philippians 1:27- 2:30
For we have an unchanging God.
For, hundreds of years before Paul wrote to the Philippians, Moses had already said to the Israelites:
this commandment that I command you today is not too hard for you, neither is it far off. It is not in heaven, that you should say, 'Who will ascend to heaven for us and bring it to us, that we may hear it and do it?' Neither is it beyond the sea, that you should say, 'Who will go over the sea for us and bring it to us, that we may hear it and do it?' But the word is very near you. It is in your mouth and in your heart, so that you can do it. (Deuteronomy 30:11-14)Neither would obedience have been too difficult nor alien for the Philippians. Plus they had (as we now also have) the example of Timothy's obedience (Philippians 2:19-23), Epaphroditus' (Philippians 2:25-30), and of Paul himself (Philippians 2:17, Philippians 1:12-26).
*Philippians 2:12-16 might seem an expansion of Philippians 1:27 - 2:4, and but given the gospel-centric-ity of Jesus (Philippians 2:6-8), God (Philippians 2:9-10), Paul (Philippians 1:19-26) and the context of the Letter to the Philippians, the emphasis seems here to be how this is lived out in the area of gospel partnership. (Not that one should Pharasaically limit its application.)