What does 1 Thessalonians 5:2 mean?

The Thessalonian believers realized the day of the Lord would begin unexpectedly, like the arrival of a thief at night. No one looks forward to a thief's invasion, so this reference is not likely a mention of the rapture. The rapture is a hopeful, welcome event, whereas the arrival of a thief is a frightful, unwelcome event. A thief comes to steal, whereas Jesus comes at the rapture to give. He gives Christians glorified bodies, a blessed reunion, and the joy of seeing him face to face (1 Corinthians 15:51–54; 1 Thessalonians 4:16–17; 1 John 3:2).

We must not think Paul's reference to the day of the Lord's coming "like a thief in the night" means that day will arrive during a literal, solar night. The comparison is not to the timing of the day of the Lord's arrival but, rather, to its manner of arrival. This era will arrive suddenly and unexpectedly. Divine judgment will catch unbelievers off-guard. They will be surprised by the sudden arrival of God's wrath.