In John 17 & 18 also, Jesus spoke about ‘true believers’ being ‘in the world’ but not ‘of the world’. And we live out our lives in the present world system, we can’t escape from it, we have to go to work, we have to pay taxes, we have to do all sorts of things which are part of the world system, but we recognize also that the present world system, whatever form it is, whatever form of government you have, is actually full of sin and, ultimately, under the power of the evil one. Satan is described in the Bible as being the god of this world.
We’re also citizens of another kingdom, the Kingdom of God, which is pure and holy, where the Lord is King. And these two systems, these two kingdoms are in conflict. Our trust is in the eternal Kingdom of God which is eternal and not in the Kingdom of this world which is passing away.