A common theme in the story of Frankenstien is revenge. When the monster is rejected by the one family he felt could accept him for who he is, he is in a state of depression and despair. To help channel his rage, the monster kills inanimate objects rather than taking them out on someone or something valuable. He does so because he is still optimistic about existence and knows that if he can find his maker, he will have a chance. At this point, the reader gets to see a more personal side of the beast. He's hurt and lonely, and he's looking for some way to be accepted. When the incident with the girl by the river emerges, the monster is shot in the arm as a reward for his goodness. He is angry, and the man who shot him swears to hold his promise until the end of the story. “I vowed everlasting hate and revenge to all humanity, inflamed by pain”. From this point forward, the monster harbors a deep hatred for humanity, especially for his maker, Dr. Frankenstein.
The creature’s hatred of mankind was mostly towards his creator, whom he wanted to feel the same feelings of pain, and desperation that he had been exposed to. Feeling rejected and abandoned, the creature seeks revenge on his creator. He needs Victor to experience isolation in the same way that he does: “I may die, but first you, my tyrant and tormentor, shall curse the sun that gazes on your misery. Beware, for I am fearless and therefore powerful.”
The creature understands that he has control over his maker, capacity to give him wretchedness, similarly as his maker has given him hopelessness. Killing Victor’s loved ones is the only idea that the monster has to make his creator feel the same as he felt.