1 Thess 5:2

5:2 day of the Lord. A prominent designation of the day on which Christ returns. It is well known from the Old Testament (e.g., Joel 2:1, 31; Amos 5:18; Zeph. 1:7, 14; Mal. 4:5), where it is used of God’s drawing near in judgment. This prominent association of the day of the Lord with judgment is carried on in the New Testament, where the last judgment and final rewards and punishments are in view (Acts 17:31; Rom. 2:5, 16; 2 Cor. 1:14). According to 2 Pet. 3:10–13, the heavens, the earth, and the elements will be destroyed to make way for a new heaven and new earth.

like a thief in the night. See Matt. 24:43, 44; 2 Pet. 3:10; Rev. 3:3; 16:15. Paul seems to be familiar with at least some of Jesus’ “Olivet Discourse” (Matt. 24:3–25:46; Mark 13:3–37; Luke 21:5–36).