The Lord is coming for those who belong to him (1 Cor. 15:23) who are waiting for the "blessed hope" (Titus 2:3). "Our being gathered to him" or the Rapture is associated with heavenly reward (2 Tim 4:8), never the judgments of the Tribualtion. Paul never instructs the Church how to prepare for it or warns us of the earthly judgments given in Mt. 24, Revelation and the Second Coming. The Thessalonians could not of been alarmed about missing the Rapture, they were reading Paul's letter of encouragement to the congregation and all were accounted for. If somebody came to your church with the same false prophecy, what would be your reaction? They were unsettled because of a false report that they were in the midst of the day of the Lord. 1 Thess. 3:3,7 confirms trials and tribulations were causing the Thessalonians to be "unsettled or alarmed." Some versions have "day of Christ" and others have "day of the Lord," with the latter being correct due to the context of this chapter. The Thessalonians were suffering trials and tribulations somewhat similar to what the day of the Lord would be like. Mentioned in this chapter is the man of lawlessness, opposition to God, works of Satan, counterfeit miracles, every sort of evil and wickedness. Surely this points to the Tribulation and that day of judgment and not to the day of Chirst and his glorious appearing for the Church. Before our gathering to him and the destruction of that day, a specific act of rebellion embodied in "the man of lawlessness" or Antichrist must be revealed in the "temple, proclaiming himself to be God." His revealing is never mentioned in the OT, Mt. 24 or Revelation, only in the Epistles that apply to the Church Age which ends before God's judgment begins. It was a sign given to the Thessslonians and the Church today that "our gathering to him" will soon follow his revealing. If the church was raptured before it, Paul's instructions would not be needed because we would not be on earth to see it.