of Jekyll. The doctor releases the evil Hyde by ingesting a potion that triggers a change. According to Wikipedia.com:

This story represents a concept...of the inner conflict of humanity's sense of good and evil. In particular [Dr. Jekyll and Mr. Hyde] has been interpreted as an examination of the duality of human nature (that good and evil exists in all), and that the failure to accept this tension (to accept the evil or shadow side) results in the evil being projected onto others...

In other words, humans, arguably, have two sides: the good and the evil. This article goes on to state that if one does not recognize the presence of a darker side, that a person's moral balance will be thrown off, resulting in "evil being projected onto others."

eNotes.com identifies another major theme as "identity:"

Dr. Jekyll disturbs the natural order of the universe because throughout his life he struggles to accept the dual nature of his identity. He determines that all of us are plagued with this duality: "With every day, and for 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 ... that man is not truly one, but truly two..."

Instead of leaning toward the good in himself, Jekyll tries to balance the two: this is the battle of good and evil, which is yet another theme. The duality of man is created by the struggle between doing what one believes is right or good, and fighting off the temptation to do that which one believes, through society and/or religion, to be evil or wrong. In trying to balance the two, Jekyll allows Hyde to get the upper hand. In giving in his evil nature through Mr. Hyde, the doctor realizes what he is doing, but also finds himself enjoying his "freedom" as Hyde (another theme).

Many of the themes in the novel point to the duality of human nature; freedom, good vs. evil, and identity all are visited in the struggle between these two opposing sides.

G. B. Stern...argues that the novel is "a symbolic portrayal of the dual nature of man, with the moral inverted: not to impress us by the victory of good over evil, but to warn us of the strength and ultimate triumph of evil over good once sin is suffered to enter human habitation."

Additionally, the concept of "duality" is seen in Victorian society at the turn of the twentieth century. Utilitarianism has found its way into mainstream society. It promotes the idea: "the greatest happiness for the greatest number..." This was also known as Benthamism—if it feels good for many, it's all right.

Contrary to the social climate of the time was the Protestant Evangelicalism movement which provided guidelines for behavior.

...the Evangelical's anxious eye was forever fixed upon the 'eternal microscope' which searched for every moral blemish...

Society and religion pull in opposite directions, demonstrating the struggle of the Victorian psyche for a balance within a state of "duality." The critical factor would apparently be the wisdom of resisting evil and leaning toward the good. If one is foolish enough to give in to evil, even believing he/she has the upper-hand, evil will successfully overwhelming good.

To understand the Victorian context of Robert Louis Stevenson's The Strange Case of Dr. Jekyll and Mr. Hyde, one must look to "utilitarianism," also known at that time as "Bethamism," a prevalent, social "belief system" in Victorian England.

One source defines utilitarianism as:

Actions are right to the degree that they tend to promote the greatest good for the greatest number.

The idea was that the pleasure of many was more important that the pleasure of the few.

eNotes.com's historical context of the novel states:

At the heart of this belief was the supposition that self-interest should be one's primary concern...happiness could be attained by avoiding pain and seeking pleasure. In Victorian People and Ideas, Richard D. Altick explains that "utilitarianism was ... wholly hedonistic; it made no allowance for the promptings of conscience, or for ... the forces of generosity, mercy, compassion, self-sacrifice, love. Benthamite ethics had nothing to do with Christian morality."

Basically, the Victorian era was about feeling good rather than feeling bad. This is a major point in the "case" of Dr. Jekyll and Mr. Hyde. Dr. Jekyll comes up with a formula that will make him stronger and fitter, however, there is a sacrifice to be made: Mr. Hyde (Jekyll's alter-ego) is much smaller, and while he has great strength, he is evil personified.

The reflection of Victorian attitudes can be seen in the following with regard to the theme of "freedom." This was especially important to Dr. Jekyll:

When he becomes Hyde he notes, 'I felt younger, lighter, happier in body; within I was conscious of...an innocent freedom of the soul.' The freedom he experiences results from the release of his inner desires, which, being a respectable Victorian gentleman, he previously had to suppress.

The theme of good vs. evil is also a central element in the story. Stevenson provides the reader with a glimpse into the struggle within Dr. Jekyll, and he is pulled between the good (morality) and evil (giving in to one's desires).

G. B. Stern in his book on Stevenson argues that the novel is 'a symbolic portrayal of the dual nature of man, with the moral inverted: not to impress us by the victory of good over evil, but to warn us of the strength and ultimate triumph of evil over good once sin is suffered to enter human habitation.'

Stevenson has written a novel of warning: the dangers of living a freely Victorian lifestyle may come at the cost of one's soul. The author, Stern proposes, warns of the power of evil to triumph when given free rein.

However, counter to utilitarianism is Protestant Evangelicalism.

Evangelicalism focused...more on the day-to-day lives and eventual salvation of its followers, [setting] patterns of conduct...to follow in order [to be forgiven] for their sins. Altick notes that "the Evangelical's anxious eye was...fixed upon the 'eternal microscope' which searched for every moral blemish...[It] is also noted for its inspiration of humanitarian activities during the Victorian age.

The Jekyll vs. Hyde dilemma may be seen as a representation of the human condition: one struggles to do what is right, is tempted by what is wrong, and must learn how to balance the two or be lost: which is what transpires in the novel. Jekyll is lost in order to save the world from the evil of Mr. Hyde: an uncontrolled aspect of Dr. Jekyll's psyche.

Additional Source:

http://webs.wofford.edu/kaycd/ethics/util.htm