Prior to this letter from Jesus, the city of Sardis had only been attacked and broken into twice in its history. A cursory look at any historical site on Sardis and you will find that in 549 BC and 214 BC the defences of the city were broken down and on both occasions it is right to believe that their overconfidence and a failure to keep watch for their enemies were the reasons for their downfall.
Jesus knows this when he appeals to the church.
“Remember, therefore, what you have received and heard; hold it fast, and repent. But if you do not wake up, I will come like a thief, and you will not know at what time I will come to you.” (Revelation 3 v 3)
He is calling them to hold on to what they have been taught, change their thinking and be alert. Otherwise He is coming and it won’t be to bless them!
This analogy of the thief we also see in the gospels as Jesus speaks of His coming. We understand the imagery.
If you knew a thief was coming but you didn’t know when what would you do? Would you cancel your life and spend the entirety not moving out of the house, not properly sleeping, afraid to leave your possessions lest the thief comes when you are away? Is that the life you would choose to live?
Or would you secure your house in readiness that the thief could come anytime? You would secure it by telling the household and even the neighbours of the thief so that you could enlist their help. You would speak often of the thief so that no one becomes complacent in waiting for him to come.
And even more importantly you wouldn’t live a blasé life. You would be diligent about your discipleship and that would involve not becoming arrogant that you would never be defeated.