As he's writing, he notices the handwriting of the text is the same as one of the other monks. He realises that all the bibles they've been copying from are, themselves, copies, and the original text must be being kept safe somewhere else. But as he writes, he makes a small spelling mistake, and starts to wonder how many other mistakes are in all the copies he's looking at.
He brings these issues up with the head monk, and he agrees it's a possibility. To settle their nerves, he tells the monk that he will examine the original text and look for any errors, then report back and try to fix the copies they've written thus far.
The next day, the monk goes to ask the head monk how things are, only to see the head monk crying at his desk with the original bible text open next to him.
"What's wrong? Was there a mistake?"
"It says celebrate."