“Some parts are literally true. Others are not. It’s important to be able to discern the difference.”
If even one word isn’t literally true, then it all goes out the window.
Who’s qualified to discern and decree truth?
Do note that it doesn't say one part is false. It says not to take a phrase or a statement in isolation from the Bible as a whole. The Bible does not contradict each other if taken in context. But if one reads only one sentence and then another random sentence, the picture one builds is wrong.
Who (individual) can discern? No one.
The Church as a community does that and has done that through the centuries.
decree -- that happens in council.
Do you know what literally means? Do you know that truth can be expressed by other means such as allegory?