What is the significance of the closing scene?

In his letter, Jekyll highlights one of the main themes of the novel, the dual nature of man. It is this concept that caused him to pursue his disastrous experiments that led to his downfall. Hyde, the personification of Jekyll's purely evil characteristics, revels in the freedom of an anonymous existence. Although he successfully distills his evil side, Jekyll still remains a combination of good and evil. Thus, when transforming back and forth, his evil side grows stronger and more powerful after years of repression, and is able to take over completely. In this way, Jekyll's experiments are the opposite of what he hoped. Interestingly, as is repeatedly mentioned throughout the novel, Hyde is a small man often called dwarfish, while Jekyll is a man of large stature. Thus, the reader is left to assume that Jekyll's evil side is much weaker and less developed than his good side. However, appearances can be deceiving. In fact, Hyde's strength far out powers Jekyll's.

In his letter, Jekyll clearly states that he felt no guilt about Hyde's actions, as "Henry Jekyll stood at times aghast before the acts of Edward Hyde, but the situation was apart from ordinary laws, and insidiously relaxed the grasp of conscience. It was Hyde, after all, and Hyde alone, that was guilty." To the reader, this explanation seems ridiculous, because Hyde is in fact part of Jekyll, and a being that Jekyll created. Therefore, clearly Jekyll is responsible for the man's actions.

In the struggle between Jekyll and Hyde, Stevenson explores the struggle of the human conscience, between good and evil, noble and despicable. Jekyll, who gives in to his evil impulses becomes a prisoner and victim of his own creation. Thus, Stevenson seems to suggest that a noble, pure life is far better than one of discreet immorality. However, Stevenson also portrays the seemingly purely noble men in the novel, Utterson and Lanyon, as weak. Lanyon dies after the shock of Jekyll's transformation, and Utterson repeatedly refuses to accept the truth or pursue the novel's central mystery. Although apparently critical of both worldviews, Stevenson seems to ultimately claim that the noble life is more admirable, as Utterson lives while Jekyll/Hyde dies.