We've heard it said to hate the world. The world is in enmity with God and therefore we must choose sides.
It sounds so harsh and unreasonable when we hear this. Perhaps it's because we don't define the world correctly.
If we see the world through the lens of the Bible, we have to define it thusly:
The world comprises all that is fallen and is fading because of sin. Included in this is the mindset that is darkened and cannot recognize the authority of God. The world represents all that is fading and unable to account for an eternal God who is bringing an eternal kingdom to those who believe in his son, Jesus Christ.
Those who love the world that is going to one day be destroyed and replaced by the new heavens and the new earth will not have room in their hearts to love the truth and cling to the one who is eternal. Just like Lot's wife who became a pillar of salt because she couldn't let go of a fallen, sinful world that was being judged, the lovers of the world will become preoccupied and hardened in their heart, unable to make their way into the coming kingdom of Jesus Christ.
The difference between those in the world and those of the coming kingdom is very simple: the world denies that Jesus Christ is the son of God who came into the world to save it. Without an eternal God providing a way for finite beings to enter into immortality, the world must savor all that it can in the wisp of time that it is given. As such the world rushes after treasures, luxuries, and comforts, because when death comes, it'll all be gone. To the world, there is this life and none other. Therefore it must, at all cost, live for today in a futile attempt to experience in a fading mist only what eternity can provide.
This is why those who belong to Jesus Christ must understand that they too must hate the world. It is fallen and engaging in all kinds of detestable abominations before the ultimate judge and creator of all things. If we are to believe in Jesus as the son of God and his word as truth, then we will do well to view the world with clear eyes and watch ourselves from being stained by it.