You have the right to be wrong, but you do not have the right to be right. Truth exists independent of what we think. If there were no people to think this or to think that, truth would still be truth.
Truth is not a matter of opinion. Let me illustrate this with two simple examples:
If I believe that the bread and the wine of the Eucharist actually become the Body and Blood of Christ and you believe they remain entirely and soleybread and wine and are only reminders of the Body and Blood, then there are two options. Either one of us is right and the other is wrong or both of us are wrong. We cannot both be right. We can love each other and respect our differing views, but we cannot both be right.
If you hold to a dispensational pre-millennial eschatology and I hold to a historic optimistic amillennialism – in other words, if you think the “End Times” are in the future and I think they culminated with the destruction of Jerusalem in AD 70 – then we cannot both be right. It is not a matter of your opinion or mine. Again, we can both be wrong, but we cannot both be right.
Some truths, like those above, substantially affect the way you live your Christian life. To live life without a recognition of the power and importance of the God’s gifts of the sacraments affects how you work with the Holy Spirit in the process of being saved. To be always waiting for a great escape from this world affects how you work for the expansion of the kingdom of God here and now and even what the kingdom of God is.
If I am wrong about these things, then I am simply wrong. If I am right about these things and you think otherwise, you are wrong.
I use these two examples because they are things about which many Christians disagree, but all remain, nonetheless, Christians. That does not make them unimportant. All truth is important.
Christian fellowship is not based upon agreeing that there is no truth or that everyone has their own truth. Christian fellowship is based upon Christ. That is why it cannot exist outside of an agreement with regard to certain truths about Christ.
Even then, what those certain truths are is not a matter of opinion. Those truths are summarized in the Niceo-Constantinopolitan Creed – what we usually call the Nicene Creed – as it was adopted by the Church at the Second Ecumenical Council in 381. It doesn’t matter which English translation of the original text is used, because the substance is not in the words, but in the meaning.
That’s why I cannot have fellowship with those who recite the same words, but have decided that they have the right to change the original meaning to suit their tastes. On the other hand, I can have fellowship with those who don’t recognize the authority of the Ecumenical Councils, but acknowledge the same truths they declared.
I can have fellowship with those who are in Christ and do not understand the truths of the Creed. I cannot have fellowship with those who disagree with the truths of the Creed, because they have then chosen to believe in someone who isn’t Christ.
Truth matters. Truth is not a matter of opinion.