Sardis

To the angel of the church in Sardis, write this:
The one who holds the seven spirits of God and the seven stars says: "I know your deeds, that you have a reputation of being alive, but you are dead. Wake up, and strengthen what remains and is about to die, for I have found your deeds unfinished before my God. Remember, therefore, what you have received and heard; hold fast, and repent.
If you do not wake up, I will come like a thief, and you will not know at what hour I will come upon you. Yet you have a few people in Sardis who have not soiled their garments; they will walk with me, dressed in white, for they are worthy. The one who overcomes will, like them, be clothed in white and will not have their name erased from the book of life, but I will acknowledge their name before my Father and His angels.
Whoever has ears, let them hear what the Spirit says to the churches."
(Revelation 3:1-6)

The church in Sardis had earned a reputation of being alive, but in reality, it had become spiritually dead. The city of Sardis had previously suffered defeat due to its complacency. Twice before, Sardis' acropolis had fallen because the city let down its guard—first to Cyrus, who defeated Croesus in 546 B.C., and later to the Cretan general Lagoras, who captured it for Antiochus the Great in 218 B.C.
In Greek cities, there was a public register of citizens, and if a person committed a crime and was convicted, their name would be erased from the list. Similarly, those who persevere in faith would have their names permanently recorded in the eternal book of life.
Sardis was known for its textile production, particularly wool used for making the himation, the most common outer garment of the time. In the Book of Revelation, the color white symbolizes purity and righteousness, making white garments the fitting reward for the victorious.