The story of Jesus's resurrection and his going into "heaven" are only the beginning of something new, something that will be completed one day, but that none of the early Christians supposed had been fully accomplished yet.That's a long quote, but he's saying simply this: The cross of Jesus characterizes the rule of Jesus. His rule and reign is spread, not through violence or war, but through proclamation and agape love. In fact, Christianity grows best when it is oppressed and persecuted--in other words, when the powers of the world do to his followers what they did to Jesus.
The early Christians were, after all, a small minority, staking their daring and apparently crazy claim about Jesus from a position of great weakness and vulnerability. They were perceived...as a threat to the established order.... But their threat to the present world was not of the usual kind. They were not ordinary revolutionaries, ready to take up arms to overthrow an existing regime and establish their own instead. Celebrating Jesus as the world's rightful king...was indeed a way of posing a challenge to Caesar and all other earthly "lords." But it was a different sort of challenge. It was not only the announcement of Jesus as the true king, albeit still the king-in-waiting, but the announcement of him as the true sort of king. Addressing the ambitious pair James and John, he put it like this: "Pagan rulers...lord it over their subjects. ...But that's not how it's to be with you" (Matt. 20:25-26). And, as he said to Pilate, the kingdoms that are characteristic of "this world" make their way by violence, but his sort of kingdom doesn't do that (John 18:36). We all know the irony of empires that offer people peace, prosperity, freedom, and justice--and kill tens of thousands of people to make the point. Jesus's kingdom isn't like that. With him, the irony works the other way round. Jesus's death and his followers' suffering are the means by which his peace, freedom, and justice come to birth on earth as in heaven.
Jesus's kingdom must come, then, by the means that correspond to the message. It's no good announcing love and peace if you make angry, violent war to achieve it!
Now, here's the point I want to make, and this applies to many Christians, particularly to those who are Reformed. The cross of Jesus replaces everything we thought we knew about what it means for God to be "sovereign" and "in control". The iron scepter that Isaiah talked about, the one by which the Messiah would rule, turned out to be the two wooden beams on which the Messiah was crucified. The sovereignty of God is most clearly visible at the cross, where the Son of God was murdered by Roman soldiers under the command of the Roman Governor, Pilate, and at the behest of the Jewish leaders. As Paul wrote in 1 Corinthians, the strength of God looks like weakness to human eyes.
If you don't perceive God's sovereignty through the lens of the cross, then you fail to perceive it at all. God does not rule with an iron fist, like a great army general; he rules like a sacrificial lamb. The rule and reign of Jesus the King is extended, on earth, through the same means by which it was inaugurated--self-giving, life-losing love. That love, the agape love of the cross, is the one force on earth that no king or general or president can ever stamp out!