The phrase "emergent church difficulties and differences", although it sounds like a new book title, is actually found in a document from 1662 known as the Propositions of the Synod of the churches of New England, which convened in Boston that year. This document was part of the affirmation of the Halfway Covenant of 1662.
Here is the quote as it appears:
"There has constantly been in these churches a profession of communion, in giving the right hand of fellowship at the gathering of churches and ordination of elders, which importeth a consociation, and obligeth to the practice thereof; without which we should want also an expedient and sufficient cure for emergent church difficulties and differences, with the want thereof our way is charged, but unjustly, if this part of the doctrine were duly practiced."
Propositions of the Synod of 1662, page 31-21, found in The Panoplist, and Missionary Magazine United, for the year ending June 1, 1812. Volume IX New Series. (italics mine)
The Halfway Covenant ended up to be quite controversial, I agree with William Hernard ["Sinners in the Hands of an Emergent Church"] that the primary reason for the termination of Edward's Northampton pastorate was his "theological position regarding a regenerate membership and the half-way covenant". I also agree with Hernard that Edwards would probably affirm some elements of the present day emergent church and dismiss others. Things have pretty much been the same since the 1600's and the age of modern missions. Once the church has experienced its own emergence (as USA did in the 1600's) and then has settled down to a more institutional existence, the only living examples of church emergence in a new culture happen overseas, out of sight, on the "foreign mission field". What we once gave permission for and blessed in an overseas context is now happening at our doorstep and in full view - the emergence of new forms of Christ's body native and contextually appropriate to a new culture, in all its 'difficulties and differences', but still true to the original intention and mandate of the One who sends us.
Hey, don't you think its hilarious that what might be the first ever reference to "emergent church" appears in a document called PROPOSITIONS of the Synod? In my research into the origins of the term 'emergent church' and its use in missiology regarding pioneer church planting situations, this is the earliest reference I have found. I would be more than happy to have someone send me information of an earlier reference.
Related: The Emergent Church, 1980