Have you looked under the hood of your car lately?  Ridiculous.  Used to be you could gap your points with a paper match and set the timing by ear.  Now you need special training, special tools.  Mostly, you need the book.  A friend who is an expert diesel mechanic told me that.  He said trucks still have the same kinds of problems they used to have but to fix them right, you have to have the book.  You can’t guess and get it right.

Psalm 19 says “the testimony of the Lord is sure, making wise the simple.”  In plain English, it means, if you follow the instructions in God’s Word, and do so with simple trust, not trying to improve on them or change them to suit what you think is best, you will wind up looking very wise. 
My mechanic friend tells me the best manual is usually the one put together by the manufacturer for its service technicians.  You can trust those.   Same thing in life.