You and I are called to live in this world but not be of the world. God has not called His people to live in some monastery away from the brokenness of the world. He has placed His people in various secular vocations in order that they may shine as lights in the darkness and be faithful to the truth of the Gospel not compromising their biblical convictions.
This is what Jesus prayed for His disciples: I do not ask that you take them out of the world, but that you keep them from the evil one. They are not of the world, just as I am not of the world. Sanctify them in the truth; your word is truth. As you sent me into the world, so I have sent them into the world (John 17:15-18 ESV).
Notice Jesus didn’t pray that His disciples be taken out of the world but on the contrary He sent them into the world to be faithful witnesses of the Gospel.
Pastor Mark Driscoll in commenting on this prayer petition wrote; “In reality, in his magnificent High Priestly Prayer, Jesus prayed against us either becoming liberals who go too far into culture and act worldly, or fundamentalists who do not go far enough into culture and act pharisaically”
There are two extremes here that we must avoid, with God’s help.

We are not to be conformed to the world by taking our cues from it’s influences, values and immoral practices. The Scripture exhorts us not to love the world, that is don’t love the lust of the flesh, the lust of the eyes and the pride of life (1 John 2:15-17). This how we are not to be of the world because we are of God and thus we love God. When the Apostle John wrote “do not love the world” he was not referring to the not loving the people of world. If that were so, then it would contradict the rest of his letter and the rest of Scripture. So there must be a way to be in the world, loving the people of the world yet not become worldly and infatuated with “the lust of the flesh, the lust of the eyes and the pride of life”. And Jesus is our perfect example to study and imitate of how to be in the world but not of the world.

I think Jesus reveals at least two things in His prayer that are crucial to being in the world but not of the world. The 1st is that we be sanctified by the truth of His word. The truth of God’s word, the gospel is to so influence our hearts and minds that it leads us into godly thinking and living. Just before Jesus prayed this prayer he told his disciples “you are clean because of the word that I have spoken to you” (John 15:3 ESV). The word of God has a powerful cleansing effect in the lives of those who are influenced and immersed in its truth. The 2nd thing is that we are to be on mission with God, carrying the truth of the gospel to the lost. Notice how Jesus in His prayer said “As you sent me into the world, so I have sent them into the world” (John 17:18 ESV). We must always remember that we are to be on mission with God. There is purpose and significance in why God has placed us where we are. Whether its our family, job, city, town, neighborhood, school, Etc. God wants us to be salt and light in those places.

So lets be about our Fathers business. Let the message of the gospel and the mission of God influence how you live your life in this world.