“Do not love the world or anything in the world. If anyone loves the world, love for the Father is not in them. For everything in the world—the lust of the flesh, the lust of the eyes, and the pride of life—comes not from the Father but from the world. The world and its desires pass away, but whoever does the will of God lives forever.” (1 John 2:15-17)
John tells us to not love the world or the things of the world. What does that mean? Why should we not love the world or the things in it?
Not from the Father. John says that the love of the world is incompatible with the love of the Father. Another way of stating this would be: we cannot have two masters. What happens when one master tells you to do one thing, but another master something different? You can only obey one; similarly, when following God conflicts with chasing the things of this world, you can only do one.
The world is passing away. John says that "the world is passing away along with its desires." When Jesus returns, the idols of this world - money, fame, power, popularity - will disappear. In Matthew, Jesus says:
“Do not store up for yourselves treasures on earth, where moths and vermin destroy, and where thieves break in and steal. But store up for yourselves treasures in heaven, where moths and vermin do not destroy, and where thieves do not break in and steal. For where your treasure is, there your heart will be also." (Matthew 6:19-21)
In the end, following these idols is futile, because they will all pass away.
What does it look like? In practice, what does it mean to not love the things of this world? Most clearly, it means making sure that our lives are lived in accordance with the God's perfect commands in the Bible - even when it means not indulging worldly desires. But at a deeper level, it means an attitude of holding things of this world lightly; being prepared to accept it when we don't get the things we want, and always giving thanks to God when we do.