Reading non-business related writings:
[In addition to the above decree against business documents] they decreed against reading any type of writing, even if it does not contain matters which are forbidden [to do on Shabbos]. Even to read it without verbalizing is forbidden.
The reason for this is: due to a decree that one may come to read, either verbally or in ones thought, layman documents.
It is forbidden to read, whether verbally or in one’s mind, even non-business related writings due to a decree that this may lead one to come to read business documents.