What does “thy kingdom come” mean?
When we say, “Thy kingdom come” – which indubitably shall come whether we desire it or not – we arouse our own desire for that kingdom by saying these words. We pray that it come to us, and we be deemed worthy to reign in it… The coming of the Lord is not loved by anyone who says that it is close at hand or very far off, but by him who, be it far or near, looks forward to it with sincere faith, firm hope, and ardent charity.
from St. Augustine Answers 101 Questions on Prayer by Fr. Ermatinger
God is creator and sovereign over all of creation; of all that is. He is the just judge (cfr. Psa 7, 93). to whom all will give an account (cfr. Rev 20:12, 22:12). Yet, His Kingdom is something that is looked forward to. Exploration of what precisely this Kingdom consists of is necessary.
The Old Testament will speak typologically of God’s Kingdom as analogous to Israel. While all the kingdoms of the earth belong to God (cfr. 1 Chr 29:11), Israel existed uniquely: And you shall be to me a priestly kingdom, and a holy nation. (Exo 19:6a) that will bring both healing to the nations (cfr. Isa 56:7) and rule over them in justice (cfr. Isa 66). God’s Kingdom will be established forever in Juda (cfr. Psa 109). While all of this shall come to pass, and in fact has come to pass in Christ, the Kingdom of God can be linked to a mighty tree of which Israel is but the seed. Even as the tree come from the seed, and not something else, but as the tree is not the seed, so too the Kingdom of God comes from Israel, not something else, is not to be truncated to Israel.
God’s Kingdom is all of creation, He is the Lord, there is no other (Isa 45:18). It exists from the beginning of creation and will continue to exist after the end of time in the Day of the Lord (cfr. Zec 14:20-21). Therefore, those “kingdoms” of creation that exist in a state of rebellion from Him (the fallen angels, the world, the nations, the flesh) do so with their respective princes because God permits them to exist so that they might declare both His mercies and His justice. In the end, all such princes will be dethroned, their time of toleration brought to an end, and there shall be only one Lord over all (cfr. Isa 45:23).
When we pray for God’s Kingdom to come, we are praying not for something that is far off (for the Lord is closer than even ourselves) or something that is close that it can be seen (for it will come as a thief in the night (1 Thes 5:2)), so as to not despair or presume, but we are praying for something that is done in firm hope. Now, this hope is firm because it is predicated upon Faith, by which we know that God is God and His Kindom, His rule, shall be overall so that all rebellion ceases. We know that it shall be, but we hope it may be established in mercy for us and our neighbors.
As individuals, we have been saved by our baptism, and through the sacraments, we are being saved, and we have this firm hope that we too might be saved. By these, we account the longsuffering of our Lord as salvation (2 Pet 3:15a). God permits the Kingdom to come as a thief to each one of us that we might prepare ourselves, that should we fall, we might rise up, but, more importantly, so the He might be glorified in us by our rejecting of our own strength and instead relying upon His grace (cfr. 2 Cor 12:10) to overcome our sins, live the life of virtue, and become perfect, as also your heavenly Father is perfect (Matt 5:48).
This, in turn, is why the Kingdom comes for the nations and the world rather than being immediately perfectly established. Our participation in Christ, the establishment of that aspect of the Kingdom within us, has us live the life of Christ as our own very lives (cfr. Gal 2:20). We have a participation in His healing and ruling of the nations. All of creation expects this and waiteth for the revelation of the sons of God (Rom 8:19). Each individual, living the life of Christ, is mandated to spread the Gospel message, to do the work of the Father for which He sent the Son and poured out the Holy Spirit. The coming of the Kingdom comes in us and through us because we are His instruments that actualizes His Kingdom. But you are a chosen generation, a kingly priesthood, a holy nation, a purchased people: that you may declare his virtues, who hath called you out of darkness into his marvelous light (1 Pet 2:9)