If you want to create random passphrases based on certain wordlists, a tool that generates these passphrases should be used rather than generating them yourself. Here comes an introduction to four different methods of creating such random passphrases.
This is a mathematical post which is related to the xkcd 936 comic about password strength. The central question is: What is better for passwords? A password containing a few random characters or a passphrase containing a (less) few random words? Here comes a mathematical discussion.