Explaining The Book of The Revelation of Jesus Christ Revelation 3 - The Letter to Sardis

Sardis, one of Asia Minor's oldest cities, was home to one of Revelation's seven churches. Sardis, which was established in 1200 B.C. was the royal seat of the prosperous Lydian Empire. The city's location, high on a plateau above the Hermus River Valley, made it essentially impregnable from below.
Revelation 3:1-6
“Write to the angel of the church in Sardis: Thus says the one who has the seven spirits of God and the seven stars: I know your works; you have a reputation for being alive, but you are dead. Be alert and strengthen what remains, which is about to die, for I have not found your works complete before my God. Remember, then, what you have received and heard; keep it, and repent. If you are not alert, I will come like a thief, and you have no idea at what hour I will come upon you. But you have a few people in Sardis who have not defiled their clothes, and they will walk with me in white, because they are worthy.
“In the same way, the one who conquers will be dressed in white clothes, and I will never erase his name from the book of life but will acknowledge his name before my Father and before his angels. “Let anyone who has ears to hear listen to what the Spirit says to the churches.