What does 1 John 2:15 mean?

Following his words to three distinct sets of believers, John instructs all three groups not to be overly attached to worldly (non-spiritual) things. Believers are to love God and one another, not the world or possessions. The term "world" is not a reference to the planet, or even to all material things. In this context, the term "world" is a reference to the fallen, man-centered system, or way of life. John gives a specific definition of this term in verse 16. Someone who loves the way this world operates, including its control by sin, is a person who cannot also focus on the Father's will.

John emphasizes this theme by saying that those who love the world, in that sense, cannot really love God. These strong words highlight the contrast between love of the world and love of the Father. Jesus offered an example of this contrast when He was tempted by Satan in the wilderness. Satan told Jesus He could rule all the kingdoms of the world—if He would bow down to him. Jesus replied, "Be gone, Satan! For it is written, 'You shall worship the Lord your God and him only shall you serve'" (Matthew 4:10).