Barnes, a commentator in E-sword, tells us:
This chapter, properly, comprises two parts: First, various practical exhortations, 1Th_4:1-12; and secondly, suggestions designed to console those who have been bereaved; 1Th_4:13-18The other commentators went into greater detail, but I figure I'll catch up with all that when I actually start studying the chapter in detail.
It sounds, from initial reading it will be filled with practical ways to live out one's faith. That this chapter will be a help to learn how one "ought to walk and to please God". The importance of walking in holiness.