Christ prayed for us to be in the world, but not of the world. Innocent as doves but wise as serpents.
In. Not of.
Being in the world means we are NOT to separate ourselves from those that need Christ. “In the world” means being exposed to the sin of the world without actually participating, yourself. It does NOT mean that we pretend like the sin of the world does not exist or that we insulate, isolate, or detach ourselves from the realities of the messiness of sin. Being in the world means engaging the messiness of our world as Christ did. We cannot be a Light to the world if we are not in it.
On the other hand, not being of the world for those that follow Christ is less well defined. We are to “become all things to all people, that by all means necessary,” that I might be used by God, for the sake of the gospel see others come to know Christ. Paul said of himself, when engaging with those who lived outside of “the law” that he was still under the “law of Christ.” We are to reach others, for the sake of the Gospel, as far as Christ will allow us to go.
These are great overriding principles, but many times, the applications are not cut and dry. He may call you to go after the one, leaving behind the 99. There is no hard and fast rule for determining when to go or who we are to go after or for what reason. Many will disagree with your approach, but they are not the ones God is asking to go.
It is difficult and messy to be in the world, but not of the world. Don’t believe me? Just try to help one person get off the street, off a highly addictive substance, or out of generational poverty or help with mental illness. I guarantee your theology of grace will be greatly shaped by your experiences as you come to love the people you are called to serve.
Be in the world, not of it.