How do I know when a doctrinal issue is important enough to break fellowship?

Al Mohler has helpfully encouraged us all to consider theological triage. Mohler distinguishes between first, second and third order doctrines. First-order doctrines are those things that

I voted #Brexit. The Supreme Court judgement is exactly what I voted for.

It is unfortunate that I need to open up with these caveats, but here we go. I did not vote brexit because I am a racist.

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