It has been many years since I dealt with dispensationalism on a regular basis, but once in awhile I will make passing mention of it and someone will ask me what it is. I tend to fumble around and give answers that are overly technical or generally incoherent, so here is my quick attempt to answer the question, "What is dispensationalism?"
Dispensationalism is a two-hundred year old strain of Protestant theology that believes the establishment of Christ's kingdom is delayed until His second coming at the end of the age. Until Christ physically returns, the world remains in a general state of corruption as the playground of Satan. The Old Covenant promises of worldwide peace and restoration will only come when the nation-state of Israel (not the "Gentile" church) is fully established and a new temple is built under Christ's direct rule. He will reign from Jerusalem for 1000 years as he brings the world under His control. After a final rebellion is crushed at the end of the millennium the eternal state will be ushered in.
Dispensationalism is the majority-report in American evangelicalism today, but represents a significant departure from historic Christendom's understanding of the already / not yet nature of the kingdom of Christ. While different branches of the church have different nuances of the what / how of Christ's kingdom, all of them believe there is a sense in which it is already here and awaiting final consummation. The church is not merely a temporary holding place for Gentile believers, but a manifestation of the new Spirit-filled temple, Christ's body, and heaven on earth. Christ will indeed come again for His bride, but His promises to the world are already being realized through the agency of His people, the church, who have been grafted into the people of Israel.
I don't believe the differences between dispensationalism and the rest of Christendom regarding the kingdom are merely academic. What Christians believe about the nature of Christ's reign shapes how they understand their own piety and the role of the church in the world. Dispensationalism leads to retreat from the world and culture because it sees it as a place of decay. Personal piety is therefore more about "quiet times" and soul-saving than earthly engagements and transformation. For the dispensationalist, the world is destined for fire, not for progressive renewal. As one radio preacher said, efforts towards cultural renewal are just, "polishing brass on the Titanic."
I want to believe that the practical implications of dispensationalism are eroding its foundations because it fundamentally opposes the work of the Spirit in and through the church. The kingdom is here in an already/not yet state whether folks want to admit it or not. The church is the Spirit-filled temple whether folks understand it or not. The body of Christ is present among us whether they realize it or not. Satan has been defeated and is being trampled even now despite ourselves. Dispensationalism is false and time will erode its influence as much as strenuous Biblical exegesis.