What it means to be clothed in white:

He who overcomes will, like them, be dressed in white. I will never blot out his name from the book of life, but will acknowledge his name before my Father and his angels. – Revelation 3:5

To be “dressed in white” means to be set apart for God and made pure. Christ promises future honour and eternal life to those who stand firm in their faith. The names of all believers are registered in the book of life. This book symbolises God’s knowledge of who belongs to him. All such people are guaranteed a place in the book of life and are introduced to the host of heaven as belonging to Christ (see Luke 12:8, 9).

(Remember, therefore, what you have received and heard; obey it, 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 3:3. The church at Sardis was urged to obey the Christian truth they had heard when they first believed in Christ, to get back to the basics of faith. It is important to grow in our knowledge of the Lord, to deepen our understanding through careful study. But no matter how much we learn, we must never abandon the basic truths about Jesus. Jesus will always be God’s Son, and his sacrifice for our sins is permanent. No new truth from God will ever contradict these biblical teachings.)

(“To the angel [banks, The Great Hall] of the church in Philadelphia write: These are the words of him who is holy and true, who holds the key of David. What he opens no-one can shut, and what he shuts no-one can open. – Revelation 3:7. Philadelphia was founded by the citizens of Pergamum. The community was built in a border area as a gateway to the central plateau of Asia Minor. Philadelphia’s residents kept barbarians out of the region and brought in Greek culture and language. The city was destroyed by an earthquake in A.D. 17, and aftershocks kept the people so worried that most of them lived outside the city limits.)

(The key of David represents Christ’s authority to open the door of invitation into his future kingdom. After the door is opened, no-one can close it – salvation is assured. Once it is closed, no-one can open it – judgment is certain.)