Disciples (my tribe, the Christian Church (Disciples of Chris)) have always held to the mantra that “unity is our polar star.” Unity between Christian traditions, local churches, and individual Christians is so important because that’s how the world will know we’re really Christ followers. But it is possible to make too much of unity at the expense of it being legitimately and authentically Christian.
The whole point of Paul’s trip to Jerusalem, he tells the Galatians in 2:4, is because of the infiltration of false brothers. The apostles and first churches cooperated because of shared gospel truth. By establishing GOSPEL unity they were also setting boundaries of that unity.
Fellowship with Christ is a sufficient basis for fellowship with one another. We must never exclude someone whom God has included in his people. But equally fellowship with Christ is the ONLY basis for fellowship with one another. Churches must not maintain unity at the price of a watered-down or false gospel.