Amen!
The passage tells us where Scripture came from, not how it is supposed to be used, but you need to look down to verse 21 to see it. I think the word “for” was added to verse 20 in the translation posted & KJV seems to have added the words “of any” in its place, which Strongs doesn’t address.
Private is only highlighted, because it was the word I used in my search.
http://cf.blueletterbible.org/search/translationResults.cfm?Criteria=private&Version=KJV