Standard rules of
Biblical English.
Not standard rules of modern English, or even 17th century English.
GT, thanks for the question!! It exposed a wonderful little secret signal about Melchisedec (thanks to Matthew's response) that I had never noticed. I had simply assumed if the name "King David" were in the Scriptures, then it would be capitalized based on the standard rules of English regarding titles. This was not so. Wow!