The passage
      v17. Paul encourages his readers to follow the example of Christian living set by himself and his team. Given the context, this example is a life of faith which rests on the grace of God, rather than one which rests on law-obedience.
      v18. Paul now encourages his readers to reject the example of the enemies of the cross. These enemies could be Jewish persecutors, or evil-livers in the congregation, but it is likely that they are "judaizers", cf. v2, 3. This group of believers held that although salvation was a work of grace through faith in Christ Jesus, a believer's standing in the sight of God was maintained and progressed by obedience to the law, ie. they believed and practiced sanctification by obedience.
      v19. These Judaizers are now described in some detail:
        i] Their end is ruin; lost spiritually. Their false doctrine will result in the loss of their standing in Christ.
        ii] They are legalistic law-keepers -"their god is their stomach". That is, they are into the minutiae of the law as a means of maintaining their standing before God. For them it is "touch not and taste not - eat and eat not."
        iii] "Their glory is in their shame" - in their nakedness. Here the reference is to their pride in circumcision. They despise those who are uncircumcised.
        iv] "Their mind is on earthly things", ie., pietistic regulations.
      So, Paul's advice is, don't follow their example.
      v20. Unlike the earthly-minded enemies of Christ, says Paul, we have a different focus. We are citizens of another kingdom. Our home is in a different place and therefore our hope is there, and so we eagerly await the coming of Christ to take us to that home.
      v21. Of course, this involves a dramatic transformation. The lowly body will be transformed into a glorious body. Our lowly body, broken by sin, weak and subjected to decay, will be transformed into a perfect spiritual body. This does not mean that all the createdness of our being is abandoned. Christ rose in human form and he has taken that humanity to the very throne of God. What we are, reflects much of what we shall be. Our transformation is into Christ-likeness. Paul deals with this transformation more fully in his first letter to the Corinthians, 1Cor.15:42-44, 49, 51-54. As for the means of this transformation, it is through the power of Christ, the power that brings everything under his control. It is the power of the Almighty God, a power that creates, transforms, and is now at work uniting all things in heaven and on earth.
      4:1 Given that we have an example to follow in the life of the apostle, given that there are enemies of the cross seeking to lead us astray, and given the hope that we look forward to and desire to share in, we must stand firm in our partnership with Christ and for his cause, the cause of realizing the kingdom of God.

Standing firm
      For Paul and the early church, the burning issue was the intrusion of the false notion that "God loves good little boys and girls". An effort-based religion is a very human creation; it is a reasonable and rational religion, but it is not the basis of Christianity. We are to proceed by grace through faith and not by effort. A religion which seeks to subdue the flesh with pietistic rules and regulations, to deny the flesh, all on the assumption that such piety maintains or progresses our standing in God's sight, is nothing more than a religion of human design.
      To deny the self of its natural pleasures for religious purposes, is to assume that God made a mistake in creating us the way he did. Why give us natural appetites if they are innately unholy? In truth, we need to live life to the full. We need to sense our being, dream, know ourselves, each other and the creation. Jesus was into work, family and home life; he came "eating and drinking". It was from the fullness of his life that he transferred life to others. Jesus did not deny life, rather he gave his life for the life of others. Only a lover of life can do that.
      We live, not because of anything we do, but because of what Christ has done for us. Our Christian life progresses, not because we deny the flesh in the obedience of piety, but because we look to the source of all life, Christ himself. In that look of faith we begin to be transformed; a righteousness of faith takes root in us. We who live, begin to live no longer for ourselves, but for him who made us. His life becomes our life.