1
general::
Be significant, indicate a great deal, as in That house of theirs speaks volumes about their income. This idiom uses volumes in the sense of "the information contained in volumes of books." [c. 1800]
American Heritage Idioms
2
general::
Phrase(s): speak volumes
Fig. [for something that is seen] to reveal a great deal of information. • The unsightly yard and unpainted house speaks volumes about what kind of people live there.
McGrawhill's American Idioms And Phrasal Verbs