The result is that healthy denominations are recognizing that their distinctives are often simply the result of a particular time and place. The members of a denomination don't need to prove that theirs is "the best" or even "most biblical", just that their ecclesiastic system works well in America in the 21st century. We can debate with others on a whole host of practical and theological matters, but in the lower-stake context of here and now, not eternally.
Looking back, we see that the fundamentalist movement of the early 20th century set the stage for this present reality. People of many backgrounds came together to set down the "fundamentals" of the faith. Now, not everything that came out of that movement was worth keeping. I think there's valid criticisms that it was reductionistic, and tended towards anti-intellectualism. However, the ideas of "various backgrounds, one faith" has quietly become the model of how different Christian groups relate to each other.
So looking at these different groups today, we can look at different denominations as outworkings of the Holy Spirt in various and sundry ways. It would be surprising if just one ecclesiastical system worked everywhere. And when we don't consider our own denomination at the be-all and end-all, we can learn from and especially be corrected by other Christian traditions. There's faith that Christendom will not come crashing down just because our own denomination adjusts its priorities or teachings. It allows us to "always be reforming", by the grace of Christ.
The outworking of all this is very practical. There's nothing in my (Presbyterian) denominational creeds that exclude other baptized Christians from fellowship or, especially, sharing with us in the Lord's Supper. There are, in fact, people from many different church backgrounds in our congregation. If those who hold to Baptist beliefs extend grace towards our congregation in their baptizing of infants (and sprinkling vs dipping), and if our congregation extends grace and consideration towards them in their decision to delay baptism, we can worship and baptize together without conflict, and we can have their older professing children baptized in our church, without anyone violating their conscience. It allows for "big tent" congregations.
Because the most important thing is that, in our local congregation, we are not divided. That we are at peace with our Christian brothers and sisters in the pew over. That we trust the work of the Holy Spirit to lead and shepherd our congregation, and also to work in the hearts of our fellow congregants. We can overlook offenses because we trust Christ. And from that foundation of Christian charity, we can extend it beyond our church, to trust the work of God's Spirit wherever people put their faith in Christ.
