I am currently reading two books that have really got me thinking about how Jesus' death, our holiness and God's kingdom all are unified: The Hole in Our Holiness by Kevin DeYoung and The Crucified King by Jeremy Treat.
Jeremy Treat argues that much theologizing on the atonement is divorced from the kingdom. What many scholars have done, as a corrective, have advocated the Christus Victor approach to the atonement (where Christ has triumphed over the forces of evil at the cross) and have downplayed the penal substitution approach (where Christ died in our place so that we might be declared righteous before God by taking on the righteousness of Christ). It is argued that the Christus Victor model lends itself more to the idea that God is bringing his kingdom than the penal view.
DeYoung's book actually doesn't talk much about kingdom (at least not yet). However, he points out that Jesus' death was to purchase for himself a people who are made holy. That was one of the ultimate goals of the atonement.
So here is my extremely quick proposal on this Saturday morning. The unifying factor between the two atonement theories and the kingdom is this: holiness.
The Christus Victor model rightly shows that Jesus overcame the forces of evil so that we do not need to worry about anything unwholesome or evil being in God's future kingdom (see Rev. 21).
The penal substitution model rightly shows that Jesus also overcomes our sinful hearts to make us holiness and make us fit for his kingdom.
So in the past I used to say that the ultimate end goal of God was this: God's people, living in God's place, under God's rule.
I think now I would modify it slightly to say "God's holy people, living in God's holy place, under God's holy rule."
One final quick note: the Puritans (of whom I am a big fan), do not talk MUCH about God's Kingdom in the future but talk often about God's rule over human hearts now. That is good.
But one thing I would also say is this: if holiness is a unifying theme between atonement and kingdom, then the Puritans, who talked often about godliness, were much more kingdom centered than we take notice of.
Our talk of holiness is kingdom talk.