1 Thessalonians 5:2 → Isaiah 2:1-4

The "day of the Lord" concept has its roots in the OT, where it refers to a future time when God will come to punish the wicked and vindicate his people, though the notion of judgment is more commonly stressed than that of deliverance—a pervasive theme throughout the prophets, with major treatments in Isaiah, Joel, Amos, Zephaniah, and Zechariah. The early Christians, for whom Jesus Christ was their "Lord," naturally applied the NT "day of the Lord" to the future time when Christ will come to punish the wicked and vindicate his followers. Paul thus far in the letter has used the term "parousia" (2:19; 3:13; 4:15), but now he switches to the phrase "the day of the Lord," most likely because, due to its predominant OT usage, it better conveys the notion of judgment associated with Christ's return. Paul sees continuity between the OT prophetic expectation of Yahweh's coming in judgment and salvation, and the Christian expectation of Jesus' return—what the prophets announced as "the day of Yahweh" is now understood as "the day of the Lord Jesus," not a different event but the same eschatological intervention, now understood christologically. This transfer of the "day of the Lord" language from Yahweh to Jesus reveals Paul's conviction that Jesus shares in the divine identity and will execute the divine prerogatives of judgment and salvation—the continuity of language underscores the continuity of God's redemptive purposes from OT to NT, now focused on and fulfilled in Jesus Christ.