So, this is the passage that brought me to 1 Thessalonians after reading Joel. The Day of the Lord is God’s just wrath poured over the evil of the world (Joel 2). The Thessalonians knew about it, and worried about when it would happen and whether their fellow believers who had died would miss it.
Paul first reassured them that even in their grief, they had hope because Jesus was with them even in death.
This part of the letter has been interpreted and taught in dozens of ways, but the heart of the message is this: Jesus is coming back and the Day of the Lord is yet to come. We don’t need to know exactly when; we should live as though it is any minute.
Matthew 24 records what Jesus said about what would precede that day: wars, natural disasters, false teachers, and all sorts of evil doing. We seem to be in that pattern of society now, but Paul added another detail: people be saying “There is peace and security” (5:3). We are most certainly NOT hearing that now.
However, that time will come and as believers, we need to remember that it is a false security led by the anti-Christ (Matthew 24:15, Revelation 13). We can be sure of this: Jesus has saved us out of that day of wrath, whether we are alive or not when the Day of the Lord comes.