How the ending of the play presents some important ideas

Priestley makes a fascinating psychological point regarding the ways people react to guilt and responsibility in this last act. The heady, breathless glee with which Mr. and Mrs. Birling react is incredibly well-observed. As more and more pieces of evidence fall into place, Birling, in particular, is so overjoyed and relieved that he even dares to imitate the Inspector’s final speech. The point, clearly, is that some people are always unwilling to accept responsibility, no matter how clearly it is explained to them. In their own heads, they will find ways out of it. Here, all it takes is to know that they are not going to be held legally responsible in order to stop worrying about their moral responsibility. It will, as the Inspector warns the Birlings at the end, take more than simply being told; they will need to be taught the moral lessons at issue here.