What does 1 Thessalonians 5:4 mean?
Paul is describing the rapture and its aftermath to the Christians at Thessalonica. Earlier, he referred to the moment when Christ will remove all believers from the earth (1 Thessalonians 4:15–17), an event now referred to as "the rapture." Following that will come the day of the Lord—in this case, a reference to the tribulation. This is a period of God's wrath and judgment on the earth.For unbelievers, the day of the Lord is a time of darkness. The prophet Joel warned about the coming of this era. He wrote: "Consecrate a fast; call a solemn assembly. Gather the elders and all the inhabitants of the land to the house of the LORD your God, and cry out to the LORD. Alas for the day! For the day of the LORD is near, and as destruction from the Almighty it comes" (Joel 1:14–15). In Joel 2:1–2 we read: "Blow a trumpet in Zion; sound an alarm on my holy mountain! Let all the inhabitants of the land tremble, for the day of the LORD is coming; it is near, a day of darkness and gloom, a day of clouds and thick darkness! …"
Fortunately for believers, the tribulation will not take them by surprise like the arrival of a thief, because believers do not belong to the darkness. First Peter 2:9 informs us that God has called believers out of darkness. Symbolically, in this passage, those who belong to the light are Christians: those who have put their faith in Jesus.