If that were true you could read the Bible through once and put it away. Nothing more to get out of it.
Instead there is something new every time you read it. People have been writing commentaries about it for 2000 years. It is still the source of new insights. There is no one interpret ion of the Bible. There are infinite interpretations.
First, there is a difference between insight and interpretation. There are many text books that I have read that I have gained new insight as I have better understood what the author was trying to convey. What the author said has not changed, but how I understand it has changed.
Second, if there are two opposite interpretations of a text, at least one must be wrong.
Third, the reasons for the "infinite interpretations" and also for the unfortunate mess of multiple denominations is that man has fallen, and brings his own sinful nature to the text and to his faith. So each interpretation is a mixture of truth and error. The question is how much of our fallen nature are we projecting on to the text.