It means the Priest and you are citizens of the Kingdom of God, the Kingdom “established by” God rather than kingdoms established by men. “My kingdom is not of this world, and they, though in the world, are not of the world. My kingdom is of (from, established by) my Father, inaugurated by Him when I was anointed at my baptism as His Son, as prophesied I would be called by King David in the Psalms. And these who follow me were granted this citizenship in my Kingdom when they were baptized.”
Peter understood this when he called us a holy nation, God’s own people, and called us as aliens and exiles in the countries where we live to live blamelessly and honorably among the peoples in the countries where we live so that our King and his Father are glorified in us.
Paul unceasingly sought to bring about the obedience of faith so that all who were baptized would be worthy of their inheritance in the Kingdom.
In his first letter, Clement writes for the assembly of God that “sojourns as aliens and exiles” in Rome, to the assembly of God that “sojourns as aliens and exiles” in Corinth.
Polycarp begins the same way to the Philippians.
And in the letter to Diognetus there is a long section describing Christians as living “in both Greek and barbarian cities, as each one’s lot was cast, and follow the local customs in dress and food and other aspects of life, (but) at the same time they demonstrate the remarkable and admittedly unusual character of their own citizenship. They live in their own countries, but only as nonresidents; they participate in everything as citizens, and endure everything as foreigners. Every foreign country is their fatherland, and every fatherland is foreign… they live on the earth, but their citizenship is in heaven…”
And, in conclusion, I am in America, but I am a Catholic (thus, a resident alien in America), I am in the world, but I am not of the world.
John Martin