Paul has more to say about living as citizens of heaven. Look at the last half of the Philippians verse, where he paints a picture of the unified body of Christ.

Above all, you must live as citizens of heaven, conducting yourselves in a manner worthy of the Good News about Christ. Then, whether I come and see you again or only hear about you, I will know that you are standing side by side, fighting together for the faith, which is the Good News.
Philippians 1:27 (NLT)

Citizens of heaven, living wherever they have been placed on this earth, share one Spirit and give their allegiance to one Lord. And when we live as citizens of heaven, then we stand side by side, fighting together to spread Christ’s Good News.

A beautiful and powerful picture of Christ’s church and unity in His Spirit and mission!

I believe that when we do live as citizens of heaven then a unity of Spirit does come. We are all members of Christ’s body. Sometimes our earthly bodies fight themselves, and they suffer and even die. We members of Christ’s body are not to fight each other. What does Scripture say? Fights and quarrels and divisions among us come from our own jealousy and selfish desires. When we live controlled by desires and motivations that come from our sinful nature, then we are living as citizens of the world, enemies of God.*

Tough words.

The Screwtape Letters, by C. S. Lewis, is a book of letters written by the devil Screwtape to mentor a younger, inexperienced demon on effective ways of tempting and tripping up Christians. This is Screwtape, warning his trainee, Wormwood, about Christ’s church (the “we” refers to Satan and his demons):

…we see her spread out through all time and space and rooted in eternity, terrible as an army with banners. That, I confess, is a spectacle which makes our boldest tempters uneasy.

We have been called to carry on Christ’s mission on this earth. If only we can look beyond our selfish wants and catch a glimpse of the great power of citizens of heaven, a “terrible army,” standing side by side and fighting for the Good News of Christ!

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* See James 4:1, 1 Corinthians 3:3