The second chapter concerns some misunderstandings that were evident among the Thessalonians regarding the return of Christ. Some of them were convinced that Jesus was going to return immediately. Because of this belief, they had quit their jobs and become idle. Paul dispelled this belief by saying that Jesus would not return until two things happened. First, the “apostasy” or the “rebellion” must occur. Secondly, and in conjunction with the apostasy, the “man of lawlessness” must be revealed. There has been much wild speculation about what Paul had in mind here. The Scriptures are the best commentary.
The most reasonable and biblical explanation of this has to do with the rise of the great persecutions from the Roman emperors in the first three hundred years of Christianity. The emperor cult grew very strong and emperors demanded that their citizens worship them as gods to demonstrate their loyalty. Those who would not do this were subjected to terrible persecutions, especially during the reigns of the emperors Domitian, Decius, and Diocletian. The book of Daniel foretold all of this in Daniel 7. The Book of Revelation confirms that it happened.
As 2 Thessalonians 2:4 states, these emperors literally placed themselves in the position of God and demanded to be worshiped. They actually built temples for their own worship and called upon people to worship them as gods. Those who promoted the emperor cult did lying signs and wonders to convince the people of the emperor’s deity. A comparison of Revelation 13 and 2 Thessalonians 2 demonstrates that “the Beast” of Revelation 13 is the same as the “man of lawlessness” in 2 Thessalonians 2. The great “apostasy” refers to the great falling away that occurred when many Christians denied their faith in the face of this terrible persecution. The entire book of Revelation deals with how Christ eventually destroyed the Roman empire and brought peace to his people.
A key passage in this chapter is 2:8-9. Here it says that Jesus will overthrow the man of lawlessness by the breath of his mouth at the splendor of his coming. The NIV translates this “by the splendor of his coming,” making it seem like we are talking about the coming of Jesus. In fact, the “coming” in view is not the coming of Jesus but the coming of the lawless one. As verse 9 begins, the text reads “whose coming is according to the work of Satan…” This does not refer to the coming of Jesus but the coming of the man of lawlessness. What the passage is saying is that at the height of his coming (the coming of the great Roman emperors) Jesus will destroy him. This is what happens in Revelation 19, which Christ and his armies destroy the “Beast” and his armies. It is talking about the destruction of the Roman empire. This is what had to happen before Jesus would return. Paul encouraged the Thessalonians to stand firm and hold to those teachings they had received from him whether in person or by letter. (Owen, Dan - Study Your Bible Online - StudyYourBibleOnline.com).