In this particular chapter we find these plagues of fire, smoke, and sulfur with these spiritual insects that look somewhat like locusts but sting and torment humans on earth.  These plagues are meant to drive people into repentance from worshipping idols and sexual immorality.  These horrible events happen to the "Inhabiters of the Earth," except for the ones who are sealed and protected by God.  This chapter is more about the good news of eternal salvation through Messiah thus avoiding the plagues, then it is about the torment and destruction of mankind.  There is mercy here.  There is grace here.  The message is to repent and turn to God for the reconciliation to Him before the final hammer falls and it is too late to do so.