As someone has already pointed out (I don’t have a link, so you’ll just have to trust I’m not plagiarizing), has there really ever been “unity” in Christianity?
Let’s go waaaay back. Peter and Paul had their beef. So did Paul and his first “official” ministry partner, Barnabas. The later had such a “sharp disagreement” (NIV) that they went their separate ways, literally, and perhaps emotionally and relationally as well. Some Jews didn’t want to be in fellowship with non-Jews (Gentiles). Some church-members were choosing “sides” amongst their pastors/ministers.
In the end though, at least canonically speaking, it really was about Jesus. How through him, everyone was one. All the major distinctions were no more (and was to be lived out in light of that understanding); “There is neither Jew or Greek, slave nor free, male nor female, for you are all one in Christ Jesus”. (Gal 3:28) Don’t be a “slave” to anything anymore, save Christ. Even Paul’s (or whoever wrote it) rhetorical slam on those who would pervert the gospel should not ultimately keep them away, but bring them back.
“But now that you know God – or rather are known by God – how is it that you are turning back to those weak and miserable principles?” (Gal 4:9)
It is sin and proneness to brokenness that creates cracks and dis-memberment in our oneness in Christ. Christ isn’t the cause.