What is the moral lesson of Frankenstein?

One moral lesson from Frankenstein is that you are responsible for the lives you create, even if you don't like the way they turn out.

The swath of death and destruction that the angry creature wreaks on Frankenstein's family and friends is the result of his rejection by his creator. Victor was his parent, even if he made his "child" out of body parts, yet he fled his child in horror, leaving him to fend for himself. Although in telling his story, Victor goes on at length about how he benefitted from a loving family, he doesn't seem to have the empathy or maturity to extend that love to a needy child of his own. As the creature explains to Victor,

I do know that for the sympathy of one living being, I would make peace with all. I have love in me the likes of which you can scarcely imagine and rage the likes of which you would not believe.

If Victor would only have offered love to his creation, so much rage and violence could have been averted.

Another moral lesson is that Victor—and the other people who encountered the creature—should have looked past his hideous appearance to try to find the good soul inside. Shelley makes the point that humans are more than our outward appearances. Yet the creature is judged by those who encounter him as an evil monster solely on the basis of his looks, without these people making any attempt to enter into relationship with him.

Finally, as the subtitle of the novel suggests, by calling Victor the modern Prometheus, too much personal ambition can lead to terrible outcomes. Victor overstepped his bounds in creating human life out of inanimate matter, if only because he wasn't emotionally ready to deal with the consequences. Shelley suggests that we should think through the actions we take, especially if they are ego based, before they cause great harm.

What lesson should Walton learn from Frankenstein?

When Walton meets Victor Frankenstein, Walton has ambitious desires as an explorer. When Victor hears of this, he reacts vehemently. He tells Walton that he should, instead of being ambitious, pursue the everyday joys of a simple life. Ambition, he warns him, will be his downfall. Victor proceeds to tell Walton his own story of ambition gone awry. He does this to try to convince Walton of the downfall that attempting to be "greater than his nature" brings to a person. He wants Walton to learn from his example not to sacrifice his life to an idea of greatness.

The novel is subtitled "the modern Prometheus." Prometheus stole fire from the gods and gave it to mankind. Because the gods wanted to keep the secret of fire for themselves, they punished Prometheus by chaining him to a rock and having an eagle eat his liver. The liver grows back every night, so that every day Prometheus has to undergo the same torture. He overstepped his limits by taking what was only the right of the gods.

Likewise, Victor overstepped his bounds and tried to be like God in creating life from inanimate matter. For this pride and ambition he too suffers punishment in form of the mental anguish of knowing he has made a mistake that has cost the lives of his loved ones. His fate is to endlessly chase the monster. He wants Walton to avoid a similar sorry and tormented future.

In response to Walton's eagerness for discovery and glory, Frankenstein says, "Learn from me, if not by my precepts, at least by my example, how dangerous is the acquirement of knowledge, and how much happier that man is who believes his native town to be the world, than he who aspires to become greater than his nature will allow." He argues, then, that knowledge is dangerous and that knowing more than we are supposed to know actually makes us miserable even though we think it will make us happy. Frankenstein wants Walton to learn this from him because it will save Walton a lot of grief and unhappiness if he can relinquish his desire for discovery and glory.

Further, Frankenstein tells Walton, "If the study to which you apply yourself has a tendency to weaken your affections, and to destroy your taste for those simple pleasures in which no alloy can possibly mix, then that study is certainly unlawful, that is to say, not befitting the human mind." In other words, Frankenstein says, if whatever intelligence Walton is pursuing causes him to give up his family and prevents him from taking joy in the things things that used to make him happy, then that is a course of action or study that he should give up.

In Walton's opening letters, Shelley characterizes the adventurer as one who is willing to risk all for his quest.  He even states that a man's life or death are worth sacrificing.  Frankenstein, of course is appalled by Walton's statement because he has experienced the consequences of an insatiable thirst for knowledge.  He cries out to Walton:

Unhappy man! Do you share my madness? Have you drank also of the intoxicating draught? Hear me--let me reveal my tale, and you will dash the cup from your lips!

Victor's desire is that Walton will realize before it is too late that his obsession with knowledge can lead only to destruction.

What is the moral of Captain Robert Walton's tale in Frankenstein?

An important theme of this play is the dangers of intellectual ambition. In many ways, Walton and Frankenstein are presented as being doubles, or characters that bear particular similtarities. The major comparison that can be drawn between them is the way that both are subject to unrestricted and dangerous ambition that threatens to push back the very boundaries of what man can do and play God. For Victor, this is of course expressed in his self-obsessed determination to create life, whatever the consequences. For Walton, his ambition is expressed through his determination to reach the centre of the North Pole and whatever land may exist there:

But success SHALL crown my endeavours. Wherefore not? Thus far I have gone, tracing a secure way over the pathless seas, the very stars themselves being witnesses and testimonies of my triumph. Why not still proceed over the untamed yet obedient element? What can stop the determined heart and resolved will of man?

It is only through hearing the tragic story of Frankenstein and what happens when ambition is allowed to reach its goal that Walton realises that unrestrained ambition is a very dangerous force, and he returns home without having reached his goal, wiser and more aware of the limits of man's knowledge and the dangers of over-reaching those limits. This is the moral of the story.