“It was thus rather the exacting nature of my aspirations than any particular degradation in my faults, that made me what I was, and, with even a deeper trench than in the majority of men, severed in me those provinces of good and ill which divide and compound man’s dual nature.”

In his final letter, Jekyll explains how, more than anything, it was his desire for achievement rather than an innate degradation in his soul that drove a wedge in his personality. What he became resulted not from his wickedness but from his scientific drive to understand what caused his split nature. Everyone, Jekyll contends, has a duality of personality and the potential for good and evil acts. Jekyll’s comparison of himself with others reveals his conviction that his evil impulses were not greater, his aspirations were higher.

With every day, and from both sides of my intelligence, the moral and the intellectual, I thus drew steadily nearer to that truth, by whose partial discovery I have been doomed to such a dreadful shipwreck: that man is not truly one, but truly two.”

Throughout Jekyll’s final letter, we see an important theme in the story: Human nature is made up of a series of oppositions—good and evil, moral and intellectual, and rational and irrational. Jekyll tries to bring moral conscience and rational analysis to investigate the central question which drove his experiment. The truth that he finds fragments his soul. Victorian society strove to separate the good from the evil in human nature to purify it. Jekyll sought to unify his soul as a natural, wholesome quest.

“I, for my part, from the nature of my life, advanced infallibly in one direction and in one direction only. It was on the moral side, and in my own person, that I learned to recognise the thorough and primitive duality of man; I saw that, of the two natures that contended in the field of my consciousness, even if I could rightly be said to be either, it was only because I was radically both.”

Jekyll makes a case for why his scientific experiment should be seen as a moral act rather than a degraded one. Jekyll had the vision to postulate a true theory about human nature only because he was so moral: He was an upstanding citizen who worked hard, became an accomplished doctor, and controlled his lower impulses. Ultimately, he says, because his good and bad sides were both fully realized, he achieved a level of consciousness that allowed him to see the truth about human nature not many others comprehended.

“If each, I told myself, could be housed in separate identities, life would be relieved of all that was unbearable; the unjust might go his way, delivered from the aspirations and remorse of his more upright twin; and the just could walk steadfastly and securely on his upward path, doing the good things in which he found his pleasure, and no longer exposed to disgrace and penitence by the hands of this extraneous evil. It was the curse of mankind that these incongruous faggots were thus bound together—that in the agonised womb of consciousness, these polar twins should be continuously struggling. How, then were they dissociated?”

Throughout Dr. Jekyll and Mr. Hyde, characters contend with the moral choices they make in their own lives and those others make around them. The theme of the duality of human nature plagues the characters, since the values of Victorian society instructed people to overcome their immoral natures. As this quote from Jekyll reveals, Jekyll’s desire to dissociate was born out of this desire to overcome his nature. Jekyll theorizes that if he were free from his lower nature, life would be more bearable, and he could live a satisfying, moral life without being hindered by dark impulses.

“And yet when I looked upon that ugly idol in the glass, I was conscious of no repugnance, rather of a leap of welcome. This, too, was myself…This, as I take it, was because all human beings, as we meet them, are commingled out of good and evil.”

In Jekyll’s last letter, the reader finally gets a firsthand account of what it was like for Jekyll to turn into Hyde. When Jekyll first sees himself as Hyde in the mirror, he sees not a monster but a friend. Jekyll strangely feels peace when facing his savage side, rather than complete repulsion. Jekyll finally accepts that he, just like every other human, has both good and evil in his or her nature. As a product of a society that encourages repression, Jekyll realizes that facing one’s own evil nature leads to peace.