John is then told that the light given to the church will influence all the nations as well as those who have authority (kings). Who are these nations and who are the kings? They are not enemy nations or hostile kings. I would suggest that the nations and the kings refer to the people of God. Here we have a fulfilment of the promise made to Abraham about the nations and royal descendants.
The people of God can be described in numerous ways. When they are described as nations, we are reminded that there will be people there from all the nations of the world and that in some way their sinless national features will remain. Yet there is not a hierarchy of nations, as if one ethnic group is more important than another.
When they are described as kings, we are reminded of the status they have – they reign with Jesus – and the focus is on their individual contributions to the life of the church as it will exist then (they bring their glory into the city). In the eternal world, there will be harmony and activity.
We are then told about two aspects of earthly life that will not exist in the church in eternity. First, there will be no night. Night-time was when the gates of a city were shut because that was the time when enemies could sneak in under the cover of darkness. In this life, the church often has nights when her enemies cause havoc. But that will not happen in the world to come.
Moreover, nothing unclean will enter the city, and this term describes people who engage in sinful practices. This is a reminder that the members of the church will then be entirely holy. In this life, it is often the case that tares are mixed up with the wheat and sometimes it is hard to tell the difference between them. Nothing sinful will exist in the future perfect church.
John is reminded that there is an exact register of the inhabitants of the city. I suppose we are being told the same point as is stated when mentioning the unclean. It is possible to be on a church roll and not to be listed in the book of life. Again, in the ancient world, the authorities did not know exactly who lived within a city (a bit like the problem today connected to immigration). But the names of the church in eternity will correspond to the Lamb’s book of life.