Historic Reformed theology has typically made distinctions when discussing the kingdom of God. Reformed theologians said there is a kingdom of power as well as a kingdom of grace/glory. (Lutheran theologians have used similar terms.) The kingdom of power is God’s general (non-redemptive) reign over all things (Ps. 103:19). The kingdom of grace/glory is God’s specific (redemptive) reign over his people (Col. 1:13). Speaking of Christ’s mediatorial reign (regnum Christi), the Reformed scholastics also distinguished between Christ’s general reign (regnum naturale or universale) and his saving reign (regnum oeconomicum).
You can typically see this kingdom distinction in historic Reformed commentaries on the Lord’s prayer’s under the second petition, “Thy kingdom come.” Here’s how Thomas Watson explains this petition (in The Lord’s Prayer, p.59).
Watson says that this petition does not speak of “God’s providential kingdom” (cf. Ps. 103:19). “This kingdom we do not pray for when we say, ‘Thy kingdom come;’ for this kingdom is already come. God [already] exercises the kingdom of his providence in the world. …The kingdom of God’s providence rules over all.” This is what Reformed theologians call the kingdom of power.
What then do we pray for in this petition?
“Positively a twofold kingdom is meant. 1) The kingdom of grace, which God exercises in the consciences of his people …We pray that the kingdom of grace may be set up in our hearts and increased. 2) We pray also, that the kingdom of glory may hasten, and that we may, in God’s good time be translated into it. …The kingdom of grace is glory in the seed, and the kingdom of glory is grace in the flower. (In other words, the kingdom of grace is “already,” while the kingdom of glory is “not yet.”)
For more information on this Reformed kingdom distinction, see an earlier post here called “The Reformed Scholastics on the Regnum Christi.” Interestingly, Abraham Kuyper also recognized these terms to some extent. (For a very closely related topic, we might also consider how Reformed theology has distinguished between God’s general providence and his special providence – terms which the WCF uses in 5.7.) In a word, and to summarize, Reformed theology makes distinctions when it comes to the topic of God’s kingdom(s).