The doctrine called trinity is not even found in the bible so why would a prophet be required to correct it?
You have by your comment proved the Wisdom of Muhammad.
Yes it is not in the Bible, but for 250 years the Christains had made it a part of the Bible, thus adding to the Word. It was made Doctrine in the 3rd Century by the Christains and has become a fundamental belief.
Had the Christains understood the Station of Christ, they would have seen Christ in Muhammad and heeded the warnings.
Just as if the Jews could have seen Moses told of Jesus. Thus the Old Rainment also has another meaning.
Regards Tony