Unity cannot be achieved around the Gospel; unity must be achieved through doctrinal affirmation.
To some extent, our problem, once again, is a flawed understanding of the doctrine as it has been presented. When referring to the Gospel, we are not simply referring to the concept of justification through faith alone (the simplistic view), but rather the fact that the whole of Christian doctrine finds its source in the Gospel and the whole of Scripture focuses on the Gospel. For example, how do we learn that God is love outside the Gospel (I John 4:10)? How do we worship without an understanding of the Gospel (“Word of Christ” – Col. 3:16)? What was the purpose of the prophecies and the moving of the Holy Spirit in the work of inspiration but to proclaim the Gospel (I Pet. 1:9-12)? Through the lens of the Gospel, there is no doctrine, whether eschatology, anthropology, ecclesiology, hamartiology, or even angeology, that remains untouched. So when a pastor calls his people to Gospel unity, he does not call them to unify around justification through faith alone (and thus to unite with Pentacostals, Presbyterians, Methodists, Luthrans, Baptists, and cool church up the block), he rather calls them to unity around the full implications of the Gospel in every area of doctrine that it touches (which is essentially analogous to the fundamentals of the faith).