Earlier, I noted how some Reformed teachers from around 1700 talked about the two kingdoms, the two-fold reign of Christ. For review, Thomas Watson, Wilhelmus a Brakel, and others like them talked about Christ’s general reign over all things and his special reign over the church. The former is the kingdom of power and the latter the kingdom of grace. As a side note, it goes hand in hand with other distinctions: common and special grace as well as general and special providence, just to name two.
Here’s Bavinck, in vol IV of his Dogmatics (the emphasis is mine):
“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 consiously and endowed with all powers gathers his church, defeats his enemies, and guides the history of the world to the day of his parousia” (p. 372).
These terms to describe the two kingdoms are standard Reformation speak. The explanation of Luther’s Small Catechism uses the exact same terms and even many of the same proof texts. This is one of those doctrines, like the law/gospel distinction, that confessional Lutherans and confessional Reformed/Presbyterians can agree upon; it is neither new or novel.