IT is readily apparent that the coming of Christ described in this chapter is not only a different event than the one in 1st Thessalonians 4. It is a different kind of an event. The rapture (during which we meet Christ in the air) will be all reunion and rejoicing. The return of Christ (which is described here) will be a day of great wrath and retribution. The rapture is for the church. This second coming of Christ will be aimed at the unbelieving world. They are different events with dissimilar purposes.
Now, it appears that someone had convinced the Thessalonian believers that the establishment of Christ's kingdom on earth had already begun. It also appears that the difficulties which they were enduring were used as proof that the time of great tribulation was upon them. In this chapter, Paul was evidently trying to clarify things a bit for them. While he certainly acknowledged the fact that they were enduring significant tribulations, he assured them that when Christ is someday revealed in all of His glory, the church will be resting, not suffering (vs. 7).
So, we really have two main topics in this chapter. First, we see the growth, security, and comfort of God's people in this era; the church. In contrast to that, we also see the miserable plight of those unbelievers who survive to see Christ's return to earth. Paul commended the Thessalonians for their faith, love, & patience. And he reassures all of us who are saints; reminding us that we will be worshipping Christ safely at His Second Coming.