What is a good thesis statement involving good and evil from The Strange Case of Dr. Jekyll and Mr. Hyde by Robert Louis Stevenson?

A good thesis statement
about good and evil from is that good and evil are not distinct from each
other but are intertwined and defined by each other. Dr. Jekyll, the quintessentially morally
upright man in the eyes of society, has long contended with the secret darker side of himself.
He writes a letter in which he explains his understanding of the dualistic nature of
humans:

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.

In other words, he
realizes that he can only be good and upright because he also has a darker and more evil side to
himself. He also realizes that all of humankind also has this duality and that good can only
exist alongside evil because it is defined by its opposite.

When Dr. Jekyll
tries to use a drug to separate his evil side, Mr. Hyde, from his good side, he finds this
situation untenable. The evil actions Mr. Hyde has carried out make Dr. Jekyll so repulsed that
he winds up killing himself. Dr. Jekyll recognizes that good and evil must exist alongside each
other and temper each other and that they cannot exist ever as unadulterated good or
unadulterated evil. It is instead our internal battle between good and evil that defines us as
human beings.