Letters to three more Asia Minor churches: Sardis, Philadelphia and Laodicea.
Sardis was a very prosperous city that specialized in wool. It was particularly known for the whiteness of its wool (the reference in 3:4 to soiled cloths is a nod to this part of their history). Sardis was also known for its defenses. The city was never taken by force. But on two separate occasions in their history the city was taken by stealth in the dark of night -- the reference to "like a thief in the night" is a play on this part of their history. The harsh criticism on Sardis is that they have the appearance of life but are in fact dead -- it is time to wake up! There is a remnant (those who have not soiled their cloths) it is time to join them.
\ Philadelphia (city of brotherly love) was a center of wine making and the prominent god of this city was Dionysus. The city sat on a major earthquake fault and was nearly destroyed in AD17 by a major earthquake. The after shocks in the first century were a source of constant worry for the residents. 3:12 -- I will make you a pillar in the temple of my God -- is a likely reference to their feeling of insecurity and instability (pillars being a symbol of strength and stability). It is worth noting that there is no rebuke to the church at Philadelphia and no call to repentance. There is simply a reminder to hold fast, be faithful, redemption is near.
Laodicea was a prosperous city and was well known for its medicines, especially an eye ointment (the reference in 3:18 to the salve to anoint your eyes is a play on that history). The city was also famous for its bluish black wool that the letter contrasts at the end of 3:18 with a call to "white robes". Laodicea was located between two sources of water. One was a volcanic fed hot spring where people would travel for bathing and medicinal purposes. On the other hill side was a deep spring fed lake where the water was cold year round. The Romans, thinking walking to these places for the cold or for the hot water was too much work, built aqueducts to carry the cold water from one side and the very hot water from the other into the center of town. When the cold arrived it had warmed and when the hot arrived it had cooled. The water in Laodicea was neither hot nor cold and was not fit for drinking nor bathing. The call to be hot or cold and not lukewarm is a direct play on this part of Laodicean history. Jesus tells them that he is standing at the door knocking (isn't that always true?). All we need do is open the door and he will come in. Jesus will not open the door. He will only enter when we invite him in.