I do not think that evangelical unity is particularly important or something to which we should aspire. Christian unity is; but Christian unity, if it is to be achieved this side of glory, will be a churchly unity. Evangelicalism is a non-churchly category. It does not organize churches. It does not ordain people. It does not disciple people. All these things are done by specific churches in specific places under specific leadership (both in terms of structure and personalities). The church is a creation of God; the parachurch is not. And Christian unity, if it is ever to be achieved on earth, requires churches talking to each other as churches. Being a pessimist, I myself doubt that such unity will ever be achieved this side of glory; but formal churchly interaction is the necessary precondition even for making it hypothetically conceivable.
Does that sound like something I would have already written and would have been savaged by conservative evangelicals and fundamentalists? You will find this in our new book, A Pure Church (order here), in the sections on unity, that aspect, much of which I wrote. You are generally never hearing today what he wrote in this paragraph.
Unity must be in the church, the local church, which is the only church. The Bible teaches unity and separation. If unity was all believers, then we could never separate. The only way for biblical unity and biblical separation to coexist is if the unity is in the church. That's also what the Bible teaches. The place of one accord, one mind, and one spirit is in the church. True unity comes from purity. Only a church has the God-given tools to keep purity, and, therefore, unity.
Now, Trueman is not obviously local only in ecclesiology. He is just stating the obvious. That's one reason he's popular. A lot of times he will say exactly what he thinks. He doesn't seem to care what the repercussions are. He's a favorite to listen to and read because of this trait. On this issue of unity, he is saying what could only be true.
The only way to keep from devaluing doctrine is by seeing unity in the church. A church can unify on all of what God said. A church comes together based on belief and practice. This is not the kind of unity of all believers. You don't see unity between all believers. You only see it in churches. Trueman sees this. He just hasn't come to the reason why or explain it. Again, our book does. Get it now while it is in prepublication. It will be out in 4 weeks or less. Buy it now!