Sardis was located at the foot of Mount Tmolus. It was the capital of the ancient kingdom of Lydia in the 7th century B.C. and became an important Persian city after it was conquered by Cyrus the Great in the 6th century B.C. By the first century A.D. the city had passed into the hands of the Romans. Although an earthquake destroyed it in 17 A.D. the city was soon rebuilt. It is believed to have been the first city in that part of the world that was converted by the apostle John's preaching. It also may have been the first city that revolted from Christianity and one of the first that was laid in its ruins.
The inhabitants of the city bore an ill repute among the ancients for their voluptuous modes of life. There may be an allusion to this fact in God's message to the church when he says: "You have a few names even in Sardis who have not defiled their garments;" (Revelation 3:4).
The fellowship in the city is the fifth of the 7 churches of Revelation given a spiritual evaluation by God Himself:
"These things says He who has the seven Spirits of God and the seven stars:
"I know your works, that you have a name that you are alive, but you are dead. Be watchful, and strengthen the things which remain, that are ready to die, for I have not found your works perfect before God. Remember therefore how you have received and heard; hold fast and repent. Therefore if you will not watch, I will come upon you as a thief, and you will not know what hour I will come upon you.
"You have a few names even in Sardis who have not defiled their garments; and they shall walk with Me in white, for they are worthy.
"He who overcomes shall be clothed in white garments, and I will not blot out his name from the Book of Life; but I will confess his name before My Father and before His angels. He who has an ear, let him hear what the Spirit says to the churches." (Revelation 3:1-6, NKJV).
What is the mysterious Book of life? We find the answer near the very end of the Bible:
"Then I saw a great white throne and Him who sat on it, from whose face the earth and the heaven fled away. And there was found no place for them. And I saw the dead, small and great, standing before God, and books were opened. And another book was opened, which is the BOOK OF LIFE. And the dead were judged according to their works, by the things which were written in the books . . .
"And anyone not found written in the BOOK OF LIFE was cast into the lake of fire." (Revelation 20:11-12, 15)
This book contains the names of those who are truly converted and saved. Those who are written in it are NOT cast into a lake of fire (put to eternal death) but are given the gift of eternal existence and considered worthy by God to enter the New Jerusalem.