1 John 2:15-18
(15) Do not love the world nor the things in the world. If anyone loves the world, the love of the Father is not in him.
(16) For all that is in the world, the lust of the flesh and the lust of the eyes and the boastful pride of life, is not from the Father, but is from the world.
(17) The world is passing away, and also its lusts; but the one who does the will of God lives forever.
(18) Children, it is the last hour; and just as you heard that antichrist is coming, even now many antichrists have appeared; from this we know that it is the last hour.
Wouldn't it be nice to be a dispensationalist and say that books and epistles such as Johns epistles are meant for a future age, and the Gospels were written for a past age? Basically all we have to draw doctrine from are Paul's epistles and revelations although. If Hebrew was written by Paul it would not count for it to is meant for a future generation according to the Dispensationalist. But I am not a dispensationalist, so when 2 Timothy says that All Scripture is good for doctrine I actually believe it!
Since 1 John 2:15-18 is Scripture and thus good for doctrine and has many implications for our lives. "If anyone loves the world, the love of the Father is not in him." It is reasonable to draw the conclusion that there is no such thing as a worldly Christian, no dual citizenship, the Kingdom of God has no allies but only enemies. So then would it be a true statement that if a man was preoccupied with the things of this life while claiming to be Christ's is a liar and not born agian? I would have to say yes, that to not crucify this life and live by the Spirit dedicated to living as a new creature fully owned by God.