The birthmark represents human mortality and imperfection, qualities of anything that is created by Nature because anything that is created by Nature can only live for a relatively short while: humans, animals, plants, and so on.  All life ends.  Further, perfection is only apparently attainable with difficult work and terrible suffering.  

In truth, no human can be perfect and be alive (according to Hawthorne) because a major characteristic of humanity is our imperfection; this is why Georgiana must have the birthmark—because she would otherwise be perfect, and this is simply not the condition of humanity.  Some people, many in fact, love her more because of the birthmark, her one imperfection; only her husband seems repulsed by it, and he is determined to do away with it.  He clearly values scientific achievement and, frankly, playing God, he values this achievement more than his wife's health and happiness.  Aylmer causes his wife a great deal of pain leading up to his removal of her "flaw."  

This quotation in Nathaniel Hawthorne’s, “The Birthmark, a major theme is man tampering with nature. Aylmer is determined to remove his wife's, Georgiana’s, birthmark, regardless that it was put there by nature or God. This quote refers to Georgiana’s birthmark as a fatal flaw that Nature has put on her to show that she will not live forever and that her perfection comes at the cost of suffering. This is Aylmer’s perception of the birthmark. He views it as a negative quality that Georgiana has been marked with, and in seeing it this way, he feels justified in his attempt to remove it. If he takes it off, she will be perfect; if her perfection must be wrought by toil and pain, then he sees himself as the one to facilitate it.