"The world" which this verse talks about isn't "the world" God so loved and that for which He gave His only begotten Son (John 3:16). It's talking about the bad fruits of worldly pursuits listed in James 4:1-3 -- fighting, quarreling, killing, coveting -- all caused by the priorities listed in 1 John 2:15, "the cravings of sinful man, the lust of his eyes and the boasting of what he has and does." If these are the things that we hunger and thirst after instead of the will of God, "righteousness, peace and joy in the Holy Spirit" (Romans 14:17) -- the priorities of the Kingdom of God, which Jesus said we must seek first (Matthew 6:33) -- then we're not trying to be friends of God. Instead, we become His enemy.