You asked what the emerging church is and where it came from. Let's see... it started in the mid-nineties with a handful of evangelical pastors and authors who started noticing a shift in our culture and began asking themselves how the church needed to change and adapt to remain relevant to this new culture. Initially the conversation revolved around "generational" differences, in other words, how to reach out the Gen Xers. But it soon became apparent that the shift was broader than just young people. Our entire culture (for the most part) had transitioned from a Modern to a Postmodern world over the past 40 years or so; so church leaders began asking themselves what church in a postmodern context would look like. Over the next decade three overlapping streams of the conversation gradually emerged.
One stream, labeled by Ed Stetzer as "Relevants", have focused on worship styles and ways of "doing church". It was assumed that to reach postmoderns we would have to make church "cool" (e.g. coffee, candles, fine art, hip music, ancient liturgical elements, etc.) However, the point wasn't to be "trendy" so much as it was the missionary impulse to contextualize the gospel and worship to the local culture - in this case, early 21st century postmodern culture. I think it's mostly a good impulse. Granted, it can get a little faddish and formulaic at times, but on the other hand, I think we should be able to embrace experimentation and diversity in the ways we worship God, and to change our old habits and traditions in order to more effectively reach non-churched people. The key influencer in this stream has been Dan Kimball of Vintage Faith Church in Santa Cruz, CA with his books The Emerging Church and Emerging Worship.
Another stream, which Stetzer calls "Reconstructionists" has been more concerned with the structures and methods of church as a whole, not just with what we do in worship. There has been a lot of talk about the problems with big, institutional mega-churches and how they can become all about the show and the systems without encouraging authentic Christian community or spiritual transformation among its members. The reaction to this brand of contemporary Christianity has led many to look for smaller, more intimate expressions of church: house churches, cell churches, incarnational communities among the poor, etc. Reconstructionists have rejected the business-like models of church structure and leadership that have dominated both contemporary megachurches, as well as the older, more traditional churches, in favor of more collaborative, horizontal models. Some of these folks can be very anti-institutional, and tend to reject entirely the very idea of paid clergy, buildings, ministry programs, and the like - though of course there are varying degrees and not all reconstructionists go to that extreme. Spencer Burke from the Ooze is probably the best example of an extreme Reconstructionist that I know of, and George Barna's latest book, Revolution, focuses heavily on this trend.
The third stream, represented by the folks over at Emergent Village - folks like Brian McLaren, Tony Jones, Doug Pagitt, and many others - is what Stetzer calls "Revisionists". However, since Stetzer means that term derogatorily, I prefer to call them "Re-Envisionists", as in re-envisioning our faith and what the gospel is really all about. This stream focuses on theological dialogue that has much overlap with the first two streams (inasmuch as worship styles and church structures are themselves theological issues). There is an openness to diverse viewpoints, and a willingness to question traditional evangelical assumptions, though there is still a deep commitment to the historic Christian faith as expressed in the early ecumenical creeds (e.g. Apostles Creed, Nicene Creed, etc.) In fact, I think the descriptors of this stream of the emerging church listed over at the wikipedia entry are actually really good:
All believers are missionaries who are sent to be a blessing to the culture around them through a lifestyle that brings God's kingdom here on earth through verbal evangelism, social activism and however God has gifted the individual.
Narrative presentations of faith and the Bible are emphasized over propositional presentations such as systematic theology which are viewed as reductionism.
An ecumenical understanding of doctrine which attempts to move beyond the conservative versus liberal impasse in Christianity while honoring the beliefs and traditions of premodern, modern and postmodern Christian denominations. This generosity also extends to dialogue with non-Christian religions and non-religious people for some emergents.
A commitment to emulating Jesus' way of living, in particular his loving of God, neighbors and those normally considered enemies. An understanding of the gospel as one centered on Christ that is a message about the Kingdom of God and reconciliation between God, man and creation.
An openness to consider a plurality of interpretations as well as the impact of the reader's cultural context on the act of interpretation in contrast to the primacy of the author's intent and cultural context. The influence of postmodern thinkers such as Jacques Derrida and Stanley Fish can be seen in the emerging church approach to interpreting Scripture.
Favouring the sharing of experiences and interactions that are personal and sincere such as testimonies over scripted interactions such as propositional, formulaic evangelistic tracts and teaching. Emerging Church participants are thus true to the social constructs of their local narratives rather than to any absolute, ahistorical, cross-cultural authority.
Creating a safe environment for those with different opinions to talk and listen with an attitude of grace when there are disagreements as opposed to the dogmatic proclamation found in historic Christianity.
Emerging Church groups also typically emphasize the following elements:
* A flexible approach to and continual reexamination of theology which causes them to see faith as a journey rather than a destination, and to accept differences in beliefs and morals.
* A belief in creating communities built out of the creativity of those who are a part of each local body.
* A holistic view of the role of the church in society. This can mean anything from a higher degree of emphasis on social action, building relationships with the surrounding community, or Christian outreach.
* Creative approaches to worship and spiritual reflection. This can involve everything from the use of contemporary music and films to liturgy, as well as more ancient customs, with a goal of making the church more appealing to postmodern people.
I would say that for me, a key shift in my understanding that has occurred thanks to the emerging church conversation is the recognition that the gospel is a lot bigger than just my own personal salvation (i.e. getting into heaven when I die). The gospel, rather, is about the kingdom of God, which is both a future hope and a present reality, and that "salvation" goes beyond forgiveness of sins to a radical transformation of my whole person as well as the whole world. This kingdom reality is about a way of life, the way of Christ, which we are called to begin following right here, right now as agents of the kingdom, working for justice, compassion, love and joy in the world around us. I have to say that this is a lot different than the gospel of personal salvation from hell, sin management, and dispensational (i.e. "Left Behind") eschatology that I grew up with. For instance, issues of social justice (e.g. care for the poor, fighting economic exploitation, overcoming racism, gender equality, care for the Creation, peacemaking, etc.) are no longer just "liberal" issues, but really are concerns that are central to the gospel message and to Christ's own mission on earth.
I hope that clarifies a little bit. Obviously this is all just my perspective, but I've been a part of the conversation for a long time now, and this is what I've observed over the years.