Victor Frankenstein can't believe he has created this creature and defied God, so he runs away from it.
To be precise, "Frankenstein" was the scientist (who was not brought back to life) and his creation was brought to life, not necessarily brought BACK to life. In the book, Dr. Frankenstein brought life to lifeless matter to create "the creature". He never actually explains how he did it. In the movie versions of Frankenstein, the creature (or monster) is usually shown to have been assembled from body parts of previously deceased people and reanimated using a bolt of lighting as a power source, but some have it achieved through some kind of chemical means.
In Shelley's original work, Frankenstein's monster was created by means of Alchemy that are not detailed in the book. In popular media, though, Frankenstein's creature is often brought to life by being stitched together out of various organic parts and brought to life by lightning.
He discovers how to animate lifeless matter
The monster was not Frankenstein, the Doctor was. Doctor Frankenstein created Frankenstein's monster.
He is repulsed.
Dr. Frankenstein is "Bewildered by the creature's story."
He is repulsed
In Mary Shelly's novel Frankenstein, Dr. Victor Frankenstein discovered the secret of life itself when he assembled his monster and brought it to life.
Victor planned to create a female companion for his creature in the Orkney Islands. He hoped that this new creature would keep the creature occupied and away from humanity. However, he ultimately destroys the female creature before she can be brought to life.
When Victor Frankenstein pumped electricity into the monster's body, the monster was brought to life.
The creature enjoyed a temporary friendship with a kindly old blind man, until the man's family saw the creature, and, seeing only a monster, drove him away. Although Victor Frankenstein created a female companion for the creature, he changed his mind and destroyed her before giving her life.
Robert Walton encounters the creature on the boat after Victor Frankenstein dies. The creature appears and reflects on all the pain and loneliness he has experienced. He then vows to end his own life by floating away on an ice raft.