Christians should live in the world, but not be filled with it. A ship lives in the water; but if the water gets into the ship, she goes to the bottom. So Christians may live in the world; but if the world gets into them, they sink.
A Christian in the world is one thing, and the world in a Christian is quite another thing. A ship in the water is all right, but when the water gets in the ship, it is quite a different thing.
Whitewashing the pump won't make the water pure.