Terry please - you seem to have picked two words and completely ignored the rest of what I wrote!
What does "one" mean?
Unity. Not other.
Singular.
I repeat UNITY does not equal UNIFORMITY!!!
There is no "one" basic doctrine of Christianity!
The central tenets of Christianity are - one God who sent Jesus Christ his son to die in order that mankind might be saved. That's all that is the united belief of one church.
Then there are different denominations which hold differing views on these central beliefs - Trinitarian/non-Trinitarian, manner of salvation ranging from universalist to 5 point Calvinism, Baptism - infant/adult/sprinkling/full immersion. Heaven/Hell/purgatory/annihilation. Pre-millennial/post-millennial rapture. Bells and smells worship to swinging from the light fittings worship. Cessation of spiritual gifts/continuation.... Yes the list of differing views goes on BUT
that's because unity does not equal uniformity!!
And guess what? I don't think God really gives a jot HOW His ONE church worships/serves Him, or about all the differences in theology as long as they give it their best shot and it's done with, yes - the RIGHT ATTITUDE! He doesn't want anyone to serve Him begrudgingly or out of duty or fear, He wants people to do it out of love for Him - these are the only two commandments, love God and love your neighbour, nothing else has to be done by force then, it all just falls into place. When Jesus told the parable of the prodigal son, he was having a dig at the Pharisees especially with his punchline at the end of the story - there were actually TWO prodigals involved. Which son do you think showed his father more respect?
Or how about this for another take - the UNITED States of America are one as a nation, under one president, yet each state can exercise its own laws eg on capital punishment, so in their unity they similarly lack uniformity.
Isn't it wonderful to have a mind of your own and not to be told what to believe or do on pain of death/hell/annihilation, by some higher power!!