Christ is a King, and an eternal one. But His reigning is not merely a matter of outward authority over in a strong political way. His reigning in the church and in eternity is by His flowing life from His throne embedded within those who have eternal life.

Compare:

"Now on the last day, the great day of the feast, Jesus stood and cried out, saying, If anyone thirsts, let him come to Me and drink. He who believes into Me, as the Scripture said, out of His innermost being shall flow rivers of living water.

But this He said concerning the Spirit, whom those who believed into Him were about to receive, for the Spirit was not yet, because Jesus had not yet been glorified."

The life giving Spirit of the Triune God is to flow out of the innermost being of the saved. This is how He REIGNS in eternity too. The picture in Revelation 22:1 shows the same flowing.

God administers the city New Jerusalem by dispensing His life out of man's innermost being, a innermost being one with the throne of divine administration.

"And he showed me a river of water of life, bright as crystal, proceeding out of the throne of God and of the Lamb in the middle of its street." (Rev. 22:1)

The street is the way to walk. River of life as bright as crystal flows the way the street goes. The throne of God is directly connected to the innermost being of the city's constituents. And they WALK according to the reigning of God's divine life flowing within them.

God reigns from within by refreshing, watering, bright clarity of His Holy Spirit. His throne of administration organically one with the innermost being of those in His eternal city.

If the above is references to Rev. 22:1; John 7:37-39 are too mystical for some of you, this might do -

"And let the peace of Christ arbitrate in your hearts, . . . to which you also were called in one Body, and be thankful." (See Col. 3:15)

Same thing.
Arbitrate - "(of an independent person or body) reach an authoritative judgment or settlement. "the board has the power to arbitrate in disputes" )

The peace of the presence of Christ, the Son of God reigning, ruling, arbitrating within. Basically the same concept of the river of life flowing in the middle of the street in the city God.