From “Growing in the character of a disciple”: Chapter 1 – What it means to be a disciple and how Christian character is formed
Another way to express the radical nature of the change we have to make, from being an unbeliever to a mature disciple, is to speak in terms of us changing our nationality. We are no longer to view ourselves primarily as citizens of the country we live in, but as people whose real citizenship is in Heaven. Jesus expects our primary loyalty to be to Him and to His Kingdom:
But our citizenship is in heaven, and from it we await a Savior, the Lord Jesus Christ
Philippians 3:20 (ESV)
Therefore, while we are alive now, we are effectively aliens or exiles. We live in this world but we are not of this world. We are to live as such, abstaining from many of the activities of those around us:
Since you call on a Father who judges each person’s work impartially, live out your time as foreigners here in reverent fear.1 Peter 1:17 (NIV)
1 Peter 1:17 (NIV)
11 Beloved, I beseech you as aliens and exiles to abstain from the passions of the flesh that wage war against your soul.
1 Peter 2:11 (NIV)
We are not to love the things of this world, i.e. the sinful, worldly things which are opposed to God and all that he stands for:
15 Do not love the world or the things in the world. If anyone loves the world, love for the Father is not in him. 16 For all that is in the world, the lust of the flesh and the lust of the eyes and the pride of life, is not of the Father but is of the world. 17 And the world passes away, and the lust of it; but he who does the will of God abides forever.
1 John 2:15-17 (RSV)
The entire population of this planet is divided into two groups – those who believe in the real God of the Bible and accept Jesus Christ, and those who don’t. All who don’t are described as being “of the world”:
1Beloved, do not believe every spirit, but test the spirits to see whether they are of God; for many false prophets have gone out into the world. 2 By this you know the Spirit of God: every spirit which confesses that Jesus Christ has come in the flesh is of God, 3and every spirit which does not confess Jesus is not of God. This is the spirit of antichrist, of which you heard that it was coming, and now it is in the world already. 4Little children, you are of God, and have overcome them; for he who is in you is greater than he who is in the world. 5 They are of the world, therefore what they say is of the world, and the world listens to them. 6 We are of God. Whoever knows God listens to us, and he who is not of God does not listen to us. By this we know the spirit of truth and the spirit of error.
1 John 4:1-6 (RSV)