This chapter contains the main purpose of the letter. The Thessalonians are wondering if “the Day of the Lord” had already begun. Paul assures them it has not. He lets them know the Day of Lord will not come until there is a general rebellion against God, led by a “man of lawlessness.” Paul tells us there is always a desire for rebellion against God, but it is restrained by something he does not name. There are those who believe that all Christians will be raptured or taken up from the earth prior to the great rebellion Paul describes here and the restraining force holding back the man of lawlessness is Christians and the Holy Spirit living within them. It appears the Thessalonians knew what Paul was talking about while we guess as best we can with the information we are given.
What is clear from the chapter is that there is a great rebellion coming. The Thessalonians were experiencing persecution, but the coming rebellion against God is going to be far worse. As we look at our world today, we see reason for both hope and discouragement. Sometimes we see evil restrained and sometimes not. Imagine a world where evil is never restrained. We should be thankful for the restraint and be part of it, but we also need to recognize that humanity will not ultimately solve its problems. Things will not be set right until Jesus returns.