Responsibility and abandonment
Victor creates a conscious being and immediately abandons him. Every death in the novel flows from that choice. Shelley uses Victor's failure to show that creating something, whether a child, a discovery, or a technology, comes with obligations you cannot walk away from.
Ambition and its costs
Victor wants to conquer death. Walton wants to reach the North Pole. The creature wants to be loved. All three pursue their goals past the point where reason would stop them. The novel shows ambition as a force that blinds people to what they are destroying along the way.
Isolation and its damage
Almost every character in the novel ends up alone. The creature is isolated from birth. Victor isolates himself to do his work. Walton is alone at the top of the world. Shelley connects isolation to suffering and moral failure again and again.
Nature versus nurture
The creature is not born evil. He becomes violent after sustained rejection. Shelley uses his arc to argue that character is shaped by environment and treatment, not fixed at birth. This was a radical position in 1818 and still generates debate.
The ethics of creation
The novel asks what creators owe to what they make. Victor never considers this question before he acts, and the novel makes him pay for that. Shelley wrote Frankenstein during early debates about scientific progress, and the question she raises, what are the limits of what humans should create, has only gotten more relevant.