In the book of Revelation, we find we are reading someone else’s mail. Jesus sent a message through John to specific churches in Asia Minor. But the Spirit has preserved these words to speak to us still today!
Sardis was a well guarded city positioned against rocky mountain terrain. Because of this, there is only a history of them being attacked two times — both times were because their watchmen fell asleep at their post, taking their security for granted. Jesus writes to the church in Sardis to say they are doing the same. They are not staying alert to the threats of the world around them — threats against their faith. They are spiritually asleep, or dead even, to the realities of the warfare happening in their midst. Jesus calls them to wake up! To stay alert and remember the good news they had received. To hold onto that and turn away from the things that have lulled them to sleep.