"There is one body and one Spirit ... one Lord, one faith, one baptism." (Ephesians 4:4-5)
Uniting in faith does not mean blending into uniformity. It means a chorus of very different believers harmonizing under the same grace. And a chorus is not a unison. Unison is everybody singing the same note, and it is thin, and any group can do it in an afternoon. Harmony is people singing different notes on purpose, and it takes longer, and it takes listening, and it produces something unison physically cannot.
We have confused those two for so long that we have started running people off for singing a third above the melody. My conviction may not be your conviction on a hundred matters that Scripture leaves open, and churches have split over things that were, in the end, preference dressed up as doctrine, with both sides sincere and both sides sure.
Unity is not agreement in every gray area. It is agreement in the things that are not gray, and grace in the things that are. There is one Lord, one faith, one baptism, and on those the church stands as one. Around those non-negotiables is a wide country of preference and secondary conviction, and there we are meant to give each other room to sing a different note. We can extend that grace. We simply have not wanted to. Learn the difference between the melody that must be held and the harmony that is allowed to differ, and stop demanding that everyone sing your exact note.