Chapter 5 of Frames "Systematic Theology" begins a discussion of "The Kingdom of God." While viewing the Covenants of God as the normative constitution of God's people, the Kingdom describes the dynamic movement of history (p87).
God could have brought the redemption, and even the final resurrection and glorification, of all mankind about in a very short time period - it seems to us. But He has decided not to.
"Why he chose to stretch out the drama of salvation over so long a time is a mystery. The length of this time is related to other mysteries of Scriptures, such as the problem of evil. We would not cry, "How long, O LORD?" if God had determined to complete his purposes in an instant, and the sting of pain and suffering would be much less if God were to abbreviate his story to a few decades. But God's decision is clear: that the history of redemption will take millenia, leaving space for dramatic movements, ups and downs, twists and turns, longings and astonishments. Salvation is to be a great epic, not a short story. God will glorify himself, not by measuring his kingdom in time spans appropriate to human kings, but by revealing himself as "king of the ages" (Rev 15:3 - NIV)." - Frame, ST, p88.
And maybe that is part of the mystery, simply that. Jesus Christ, we find, is King of kings, and Lord of lords, measuring that Kingship and Lordship over epochs of time and space. We will see it far more clearly then, at the end, that Jesus was Lord of all. But we will see it because it will have dynamically taken place in the time and space He created.