May the God of endurance and encouragement grant you to live in such harmony with one another, in accord with Christ Jesus. — Romans 15:5
The gospel cannot puff us up. It cannot make us prideful. It cannot make us selfish. It cannot make us arrogant. It cannot make us rude. It cannot make us gossipy. It cannot make us accusers. So the more we press into the gospel, the more the gospel takes over our hearts and the spaces we bring our hearts to, and it stands to reason, the less we would see those things antithetical to it.
You cannot grow in holiness and holier-than-thou-ness at the same time. So a church that makes its main thing the gospel, and when faced with sin in its ranks doesn't simply crack the whip of the law but says "remember the gospel," should gradually be seeing grace coming to bear.
It works out this way individually. The most gracious people you and I know are people who have had an experience of grace and fixate on grace. The least gracious people we know are people who may know about grace academically, "theologically," but don't seem the least bit changed by it and really have a fixation on the law. They have an inordinate fixation on who did what wrong and what they deserve.
The same dynamic takes place in churches. Where grace and law are taught academically but law is "felt" as the operating system of the church, you will likely have a stifling, gossipy, burdensome environment. Where grace and law are taught theologically but grace is felt as the operating system of the church, you will see people begin to flourish, breathe. (You'll also attract more sinners, which is where religious people start getting a little antsy.)
But the message of grace made preeminent will generate an atmosphere of grace.
This is why the harmony with each other of Romans 15:5 is "in accord with Jesus Christ." It's not predicated on having a bunch of stuff in common. It's not predicated on common race or social class. It's not predicated on a common special interest or political cause. It's not predicated on all being theology nerds, liking the same authors, being Reformed or Arminian or somewhere in between. It's not predicated on all being Republicans or Democrats. It's not predicated on all being for social justice. It's not predicated on all being homeschoolers or public schoolers. It's not predicated on music styles or preaching styles or anything like that. All of that sort of commonality produces a very fragile harmony.
It is instead predicated on our common Savior, Jesus Christ, compared to whom we are all sinners who fall short of God's glory, and from whom we have all received grace upon grace. It's impossible to bask in the glorious grace of Jesus Christ and at the same time toot your own horn. So the more that we together focus on the gospel of Jesus, the more together we will walk in accordance with him and therefore in harmony with one another. "Gospel doctrine," Ray Ortlund says, "creates a gospel culture."