In chapter four, of Mary Shelley's Frankenstein, Victor tells readers of the painstaking process of collecting the pieces needed to make his "son." His utter excitement can not be seen in any other place than the following excerpt:
A new species would bless me as its creator and source; many happy and excellent natures would owe their being to me. No father could claim the gratitude of his child so completely as I should deserve theirs.
Here, Victor's desire to create life stems upon the blessing his "child" would bestow upon him as its "father."
In chapter five, when the being first comes to life, Victor's feelings change dramatically.
How can I describe my emotions at this catastrophe, or how delineate the wretch whom with such infinite pains and care I had endeavoured to form? His limbs were in proportion, and I had selected his features as beautiful. Beautiful!—Great God!
Victor's rejection of his "child" is based upon the fact that he had toiled night and day, at the cost of his own health and family, to "birth" his "son." Upon seeing his "son" come to life, the pieces which he chose for their beauty became horrifying to him. The pieces, sewn together, did not have the beauty they did when they existed as individual parts.
Horrified by his "son," Victor flees from his flat. Later when he returns with Henry, Victor hopes that the creature is not there. Victor, with these hopes, alienates his "son." His concerns no longer lie in reanimating life. Instead, his concerns revolve around never seeing his "son" again.
Essentially, Victor rejects his "child" because he considers it a catastrophe.
Frankenstein is appauled by his "child". He believed that by creating a being made of the most beautiful parts, the product would be beautiful, but when the monster wakes up, Victor sees what he has created and knows that what he has done is wrong. The creation of an unnatural being, by unnatural means disgusts Victor and that causes him to flee.