The world, Satan’s kingdom and even the physical world, is passing away. It has been cursed by God since the fall and is subject to the principle of decay, so that human beings who have turned away from God and made an idol of the creation can never find satisfaction in it.
It is foolishness for a human soul to attach itself to anything that is less enduring than itself. God is the only source of life and satisfaction for those possessing eternal life.
How can John say that we abide forever when all face death at the end of life? Every believer has Christ’s promise that he will never see death. At the end of life the soul goes straight to be with the Lord and the body sleeps in the grave until the resurrection, but at no point are we separated from the Lord.