When you become a citizen of heaven, you become a foreigner on earth. That means this earth is like a transit lounge in an airport: this isn't where you're going to spend the bulk of your time. You're just passing through. With that in mind, let's look at some characteristics of heavenly citizens from Philippians 3:
1. Citizens walk with partners: "Brethren, join in following my example" (v. 17). Paul wasn't putting himself on a pedestal here; he was placing himself on a platform next to the Philippians and saying, "Join me in this pursuit of Christ" (see also 1 Corinthians 11:1). Paul then moved beyond his own example and said, "Note those who so walk, as you have us for a pattern" (v. 17). We need people who have walked the Christian life before us or who will walk beside us and show us how it's done.
2. Citizens watch for pretenders: "For many walk, of whom I have told you often, and now tell you even weeping, that they are the enemies of the cross of Christ: whose end is destruction, whose god is their belly, and whose glory is in their shame—who set their mind on earthly things" (vv. 18-19). Not everybody within the borders of a country are loyal citizens. Paul knew this was the case even in the church (see Acts 20:29-30).
3. Citizens wait for a place: "For our citizenship is in heaven, from which we also eagerly wait for the Savior, the Lord Jesus Christ" (v. 20). Citizenship is the Greek word politeuma, where we get our word politics. In other words, Paul was saying, "Our political affiliation is in heaven." That's one way to tell if a person is really a citizen of the kingdom: they can't wait to see the King, and they wait for Him eagerly.
4. Citizens will get a promotion: Christ "will transform our lowly body that it might be conformed to His glorious body, according to the working by which He is able even to subdue all things to Himself" (v. 21). One day the Lord will give every citizen of the kingdom of heaven a body that will be like Jesus' own resurrected, glorified body.
To sum it up, look around for good examples to follow, look out for imitations to avoid, and look up for Jesus to return.
The Lord wants you to be absolutely sure as you live on earth that your citizenship is firmly fixed in heaven. So is your faith in Jesus Christ alone? Is your name written in the Lamb's Book of Life? Has your passport, so to speak, been stamped by the blood of Jesus?