For you yourselves know perfectly that the day of the Lord so comes as a thief in the night.
All Commentaries on 1 Thessalonians 5:2 Go To 1 Thessalonians 5
Augustine of Hippo
AD 430
So what is this day which the Lord has made? Live good lives, and you will be this day yourselves. The apostle, you see, was not talking about the day which begins with sunrise and ends with sunset, when he said, “Let us walk honorably, as in the day”; where he also said, “For those who get drunk are drunk at night.” Nobody sees people getting drunk at the midday meal; but when this does happen, it is a matter of the night, not of the day which the Lord has made. You see, just as that day is realized in those who live godly, holy and righteous lives, marked by moderation, justice, sobriety. So too on the contrary, for those who live in an ungodly, looseliving, proud and irreligious manner—for that sort of night, the night will undoubtedly be a thief. “The day of the Lord will come just like a thief in the night.” ..