“To the angel[a] of the church in Sardis write:
These are the words of him who holds the seven spirits[b] of God and the seven stars. I know your deeds; you have a reputation of being alive, but you are dead. 2 Wake up! Strengthen what remains and is about to die, for I have found your deeds unfinished in the sight of my God. 3 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 3:1-3 NIV)
Some popular churches may be good churches. But the Church at Sardis was not. Jesus bluntly tells its congregation that “you are dead” even though “you have a reputation of being alive.” Jesus commands them to repent and start doing what is right (which undoubtedly means that they needed to turn their focus back to the Christ-centered Gospel).
Jesus threatens that if they do not “wake up” that “I will come like a thief.” This seems to imply that some of them are not saved, and if they do not repent He will come and punish them, i.e. literally throw them into hell. The New Testament teaches that the Day of the Lord will “come like a thief” for unbelievers to punish them for their wickedness and unbelief (I Thessalonians 5:1-3, II Peter 3:10). Jesus will only come as a thief for unbelievers, for a thief is someone who does damage. He will not come as a thief for true believers, because they are joyfully anticipating His return; it is not something horrible that catches them off guard (I Thessalonians 5:4)
Here is how the Bible describes Jesus’ return for believers:
For we believe that Jesus died and rose again, and so we believe that God will bring with Jesus those who have fallen asleep in him.15 According to the Lord’s word, we tell you that we who are still alive, who are left until the coming of the Lord, will certainly not precede those who have fallen asleep. 16 For the Lord himself will come down from heaven, with a loud command, with the voice of the archangel and with the trumpet call of God, and the dead in Christ will rise first. 17 After that, we who are still alive and are left will be caught up together with them in the clouds to meet the Lord in the air. And so we will be with the Lord forever. 18 Therefore encourage one another with these words. (I Thessalonians 4:14-18)
In contrast, here is the description of Jesus’ return for unbelievers:
God is just: He will pay back trouble to those who trouble you 7 and give relief to you who are troubled, and to us as well. This will happen when the Lord Jesus is revealed from heaven in blazing fire with his powerful angels. 8 He will punish those who do not know God and do not obey the gospel of our Lord Jesus. 9 They will be punished with everlasting destruction and shut out from the presence of the Lord and from the glory of his might10 on the day he comes to be glorified in his holy people and to be marveled at among all those who have believed. This includes you, because you believed our testimony to you. (II Thessalonians 1:6-10)