Regarding the letters to the seven congregations in Revelations, the letters are to the ANGELS of the seven congregations. If you notice, God is telling the ANGELS about the good AND the bad that can be found in the PEOPLE that make up the 'congregations'. Another thing that I think is worth noting, some of the PEOPLE in the 'congregations' seem to hold teachings that aren't scriptural in any way. I think that the 'congregations' themselves represent ALL of mankind. Even Antipas (Pilate) is refered to as being "my witness, the faithful one, who was killed by your side", which is previously revealed as being "where the throne of Satan is". I don't think that these letters in any way indicate that there is one "specific" Christian organization that the messages are meant for.