For me:
-if I wanted to know all about what was "behind" the MESSAGE itself, or the "true meaning" of the message itself, I would take the 1st house as signifying the message (it would be the "subject matter" of the investigation into the causes behind it), then the 3rd house (for more info about the message) and finally the 9th house (for truth or falsity of the message)
-if I wanted to know about the PERSON/PERSONS who sent the message to me, I would take the 1st for querent (me), the 7th for them (person/persons who sent it), 3rd from the 7th for what they were trying to communicate, and the 9th from the 7th to determine if what was in the message were true/honest/accurate, or otherwise.