'Each successive generation of the church has the privilege of living as though it were the generation that will greet the returning Christ.'
I enjoyed this quote from the late, great F. F. Bruce on Philippians 3v21; it brings home the reality I think Paul is trying to convince the church in Philippi of. He is quite bluntly reminding them that their citizenship is in heaven; that is where they belong, that is where they are going, and therefore their lives should be heavenbound-shaped.
Philippians chapter 3 seems to be a crucial lesson in standing firm (4.1), and one of the ways you stand firm is by having a clear understanding of where, as a Christian, you're headed. His model of discipleship is one of straining forward, every muscle and fibre working towards the goal of heaven. The danger of Philippians 3 seems to be mindsets that are in opposition to that: both a kind of religious perfectionism highlighted by his strong negatives in 3.12 & 13, and a wordly here-and-now grab-it-all approach seen in those whom he calls 'enemies of the cross of Christ' (3.18).
The solution is remembering your citizenship is in heaven - not of Philippi or Rome, London or Earth. We await a Saviour, who will transform our bodies of humiliation to be bodies of glory, for He is the name above all names to whom everyone will one day bow. Because that is our destination we can live Christ-minded sacrificial, neck-on-the-line striving for the gospel lives that Paul advocates in the rest of the letter.
I'm challenged by this. We often talk about living in light of eternity, but for Paul this means a very practical change in our priorities and goals here and now. One of the striking things about his letter to the Philippians is that, whilst soaked in the language of Christian love, joy, and delight, Paul sees this happening in the face of cross-shaped living: standing up for the gospel, facing hardships, and foregoing 'rights'.