It's a Roman phrase and conception. While I'm sure most of you would agree as to what such a thing means on the political sphere, I'd rather not delve into such for my own sake. That Christ is King is a given, really. That that has implications in the world is also a given. However, I doubt that anyone will fully understand what those implications are. Thank God for the future consummation of the heavens and the earth, for then I'm sure we will understand.
Christ is priest prophet and king, surrender to the kingship of Christ would lead to social justice and peace
He is king of both heaven and earth. Imagine the harmony which would ensue if man were to surrender to the absolute authority of Christ The King
To add to @Aidan's point I also think that the Christian regeneration and a holy life will lead to a visible difference in this world, not just the next.