You know, it just struck me that the word "extract" could easily be "strain" or "sift". But what happens if the sifter has unrepaired tears in it from past snags. What if the sifter is corrupt from a life of sin? And what if it's a strainer of my own making? I wouldn't know what to cast out and what to keep. So, I end up with a faulty strainer that has holes in it that lets things through that should stay out.
I cannot define what is precious and what is worthless. If I do, my strainer will never be pure and trustworthy. God has to define my terms; His Word MUST be my strainer, otherwise, I'm just as blind as the Israelites were.