The Thessalonian converts were shaken and disturbed, convinced that what they were seeing was the great and awesome day of the Lord, possibly from a forged letter from Paul, according to The Scofield Study Bible III: See Joel 2:31, Joel 1:15, Revelations 19:19 which they were taught to expect deliverance on the day of Christ (the time of gathering too Him. See 2 Thess. 2:1). This letter to was written to actually instruct the Thessalonian Christians that the gathering together to Christ (I Thess. 4:14-17, 2 Thess. 2:1) will actually precede the Day of the Lord.