The debate running over here regarding spiritual and physical kingdoms seems to me to be getting confused. To my mind, a straightforward distinction needs to be made between the place where the king is and the place where his reign takes effect.
Jesus became Israel’s king by his resurrection and exaltation to the right hand of God, from where he would rule until all his enemies have been placed under his feet. It’s misleading to call this a “spiritual” rule—the New Testament doesn’t; “heavenly” would be a better term. It’s a rule enacted from heaven.
But this reign at the right hand of God has a real world impact; it is directed towards realities on earth. “Your will be done on earth as it is in heaven….” It cannot be separated, in my view, from such events as the destruction of Jerusalem, the defeat of classical paganism, and the deliverance of the churches from persecution, just as, for example, God’s heavenly rule in Isaiah 52 is apprehended in the historical event of the return from exile.
Certainly faith comes into play here, but not because this is an invisible, spiritual kingdom that only some people can see. Faith is necessary because the concrete historical demonstration of the fact that Christ has been given the authority to judge and rule is deferred. The early church believed that at some point in the foreseeable future things would happen on earth as a consequence of what God had done through Jesus. When Jesus is finally revealed as king, when he “comes” to vindicate his followers, those who did not believe the gospel about God’s Son being made Lord will be punished. But what this apocalyptic narrative referred to, I suggest, was every bit an earthly, historical state of affairs.
The point of the thief in the night simile is not that some people won’t notice that it has happened. It is that it will happen when people are least expecting it:
While people are saying, “There is peace and security,” then sudden destruction will come upon them as labor pains come upon a pregnant woman, and they will not escape. (1 Thess. 5:3)
Paul is certainly not suggesting that some people won’t notice the “sudden destruction” from which “they will not escape”.
So I recommend ditching the spiritual/physical distinction. It misses the point. The kingdom of God in the New Testament is as worldly as it ever was in the Old Testament. The difference is that Jesus, a crucified messiah, has been given authority to exercise that rule from his exceptional position at the right hand of the Father.