What literary technique is Hawthorne using when he writes that hesters "sin, her ignominy, were the roots which she had struck into the soil"? What does this comparison add to the overall effect of the passage?

Hawthorne is using metaphor in this passage. This tells us that Hester's sin was organic to her being. Hester had Pearl as a conscious decision to follow her passion and create something that was true and beautiful. Hawthorne uses earth and life imagery to make this comparison.