In historic Reformed theology the doctrine of Christ’s kingdom(s) has usually been discussed like this: Christ is king generally over all things (this is called the kingdom of power). More specifically and savingly, Christ is king over his people (this is called the kingdom of grace [here and now] and the kingdom of glory [the new creation]). Here’s how Francis Turretin (d. 1678) explained the kingdom(s) of Christ. (I’ve edited it slightly for length).
One kingdom of Christ is natural or essential. He is king over all creatures with glory and majesty equal to that of the Father and the Holy Spirit. This kingdom extends over all creatures and is founded on the decree of providence. This kingship is exercised by Christ inasmuch as he is God and the Logos. This kingship belongs to Christ by nature, which is why this kingdom is his natural kingdom.
The other kingdom of Christ is mediatorial and economical (that is, having to do with the economy of salvation). He exercises this kingship in a peculiar manner as God-man; it has everything to do with the church. It is founded upon the decree of election. It is called his mediatorial kingship because it is a dominion peculiar to the Mediator according to grace and salvation. God constituted Christ as King over the church. (Institutes of Elenctic Theology, 2:14.XVI.)
Around 225 years later, Herman Bavinck (d. 1921) discussed the kingdom(s) of Christ in almost the exact same way.
“The kingship of Christ is twofold. On the one hand, it is a kingship of power (Ps 2.8-9; 72.8; 110.1-3; Matt 28.18; 1 Cor 15.27; Eph 1.21-22; Phil 2.9-11, etc). In order that Christ may truly be king over his people, the king who redeems, protects, and preserves them, he must have power in heaven and on earth, over Satan and the world. It is a kingship of power, subordinate to, and a means for, his kingdom of grace” (p. 371).
“On the other hand, the kingship of Christ is a kingship of grace (Ps. 2.6; Is 9.5-6; Jer 30.9; Ezek 37.24; Luke 1.33; John 18.33ff; Eph 1.22, etc). …For it is a kingdom of grace in which Christ rules by his word and Spirit. …It is the living Christ exalted to sit at the right hand of God who consciously and endowed with all powers gathers his church, defeats his enemies, and guides the history of the world to the day of his parousia” (Dogmatics, IV, p. 372).
If you’re still interested, Thomas Watson (d. 1686) echoes these same things in The Lord’s Prayer (click here to read more). As I’ve said here before, no one can fault Reformed theology for ignoring or downplaying kingdom theology. We’ve always talked about Christ’s two-fold kingdom. When we say “Christ is King!” it is a confession full of meaning, theological depth, and beauty.
rev shane lems