There are more than 3 verses that call for unity. Each person is his own authority. Each person has to decide for them self what is a true principle.
Pop Quiz: 1. what language are the books of the New Testament written in?
2. what was the language of the people spoken in Judea during the 1st century c.e.?
3. what language are we speaking here today?
If we just deal with the problem of language when trying to determine meaning, it's easy to see how many people will have different interpretations when they are reading a verse written in another language a long time ago. This happens all the time with literature....just last year, there was a whole new English translation of War and Peace created, because some Russian/English scholars had been feeling for a number of years that English readers were missing a lot of what Tolstoy was trying to get across with that book. Same thing happened in philosophy at the start of the 20th century, when Bertrand Russell, Wittgenstein, and some of the other major German and English philosophers realized they were at an impasse in trying to further develop various areas of philosophy because of the differences in their languages.
I'm not saying I personally accept as a given, that the Bible is inspired -- but those who do have to realize that modern translators can't claim divine inspiration, and there will be at least some differences regarding interpretations of certain verses, and how they relate to other verses in the Bible. If the differences can't be completely resolved to everyone's satisfaction, it would make more sense for the majority to say:"we all agree on what's crucial to being a Christian, but we have a few differences regarding the details." The alternative are those who declare:"we're the only ones who are right and everyone else is wrong," and that may not necessarily lead to the 100 Years War; but there will always be the potential for religious differences adding fuel to the fire during a time of conflict.
I think this policy of inclusion is going too far. I will wager that if I were to say (and this is just for arguments sake) that Jehovah's Witness are Christian Many would judge them not Christian and not tolerate that opinion. But people have no problem with 2 churches that differ on "minor" differences. I see no difference as "minor". Everything matters to God otherwise Galatians 1:6-8: would not be in the Bible.
What I don't get is how one can tolerate the mainstream Churches differences and reject the "Jehovah's Witness" type churches. What authority made that decision? There seems to be some major hypocrisy here.
I am very familiar with Jehovah's Witnesses, since it's the religion I left home to escape from! Or, as a caveat I should say I'm familiar with what they used to say and believe in back in the 70's, since I am told a lot of things have changed since then. Regardless, I still hear that they consider themselves to be Jehovah God's one true church (they attach great significance to using the YHVH name for God in the Hebrew scriptures); so I don't think J.W.'s, Mormons, Mennonites, Seventh Day Adventists, or other churches which make an exclusive claim that only their churches are truly Christian and have God's favour, could or would want to be part of some larger Christian ecumenical movement. Now, as for how to deal with the churches who say "we're the real church, and the others are Christian, but not quite as good as us," I would say it would make more sense to put the emphasis on the unifying factors, rather than try to drive a wedge in and divide...but that's my opinion.