That it is the pure, perfect, exact words of God. It isn't; it's just a translation. If you have proof -- real, verifiable proof that it is the pure, perfect, exact words of God.-- then let's see it. Don't just take a quote out of context -- two verses from a single psalm -- and say that applies to a translation created thousands of words later.
How about 2 Peter 2:1? "But false prophets arose among the people, just as there will be false teachers among you." How do we know you're not just teaching falsely, as Peter prophesied.