Familiarity breeds contempt… or so they say.  Basically the longer you have something or someone in your life, the easier it is to take them for granted. As John writes to the churches who are probably a few generations old now, he desperately wants them to recognise that it is very easy to take Jesus for granted… to get bored of Jesus and chase after something else.  So John takes a moment to remind the people just how powerful the gospel is compared to the attraction of the world.

1 John 2:12-17

I am writing to you, little children,
    because your sins are forgiven for his name’s sake.
I am writing to you, fathers,
    because you know him who is from the beginning.
I am writing to you, young men,
    because you have overcome the evil one.
I write to you, children,
    because you know the Father.
I write to you, fathers,
    because you know him who is from the beginning.
I write to you, young men,
    because you are strong,
    and the word of God abides in you,
    and you have overcome the evil one.

Do not love the world or the things in the world. If anyone loves the world, the love of the Father is not in him. For all that is in the world—the desires of the flesh and the desires of the eyes and pride of life—is not from the Father but is from the world. And the world is passing away along with its desires, but whoever does the will of God abides forever.