Dr. R. Scott Clark of Westminster Seminary California does a nice job discussing The Kingdom of God as it relates to the visible church in the following webcast. It is a short discussion (about 15 minutes) but covers all the bases concerning the nature of God's kingdom and how that relates to the church and its members. Click on this link to listen: Heidelcast 14 Feb 2010: The Kingdom of God and The Visible Church
Behind this discussion is a larger debate in the reformed world: Is everything a Christian does "kingdom work?" Aren't Christians called to transform culture? Is God's kingdom "merely" spiritual or will there be some visible manifestation of it in this world? Clark answers all of these questions and more by referring to the Heidelberg Catechism and the Westminster Larger Catechism. His comments are charitable and reveal an understanding of this topic that is identical to that of Calvin, Ursinus, and the Westminster divines.
I must confess that my entry points into reformed theology left me muddled over these questions. For all the talk about transforming culture I see little manifestation of real change. For those who prefer the 'dominion' motif I answer the same way: "Where, in the last 2,000 years of church history have we seen lasting dominion?"
Listen to the entire webcast for at the end Clark uses a very helpful analogy to explain the topic.