The ambiguity of Pearl's background is a clever topic to add to the supernatural accents that surround the atmosphere ofThe Scarlet Letter.
First, in chapter 6 Pearl is surreptitiously described as
...that little creature, whose innocent life had sprung, by the inscrutable decree of Providence, a lovely and immortal flower, out of the rank luxuriance of a guilty passion.
This gives Pearl an air of mysticism that reminds the reader that Pearl's existence is a product of sin and fate: have these two elements combined to create an altogether different creature?
Even Hester seems intimidated by Pearl. This is what leads her to ask Pearl whether she is her daughter, and who sent her to her. To this, Pearl responds by asking her mother to tell her the answer herself. When Hester talks about Pearl being sent from "Our Heavenly Father", Pearl answers a very surprising
He did not send me! cried she positively. I have no Heavenly Father!
This statement reinforces the Puritan idea that children that are illegitimate are what the villagers called a "demon offspring".
Second, this ambiguity also makes Pearl seem even more enigmatic. In chapters 7 and 8, during Hester's visit to the magistrate, Pearl demonstrates that she is not a typical child. She taunts and teases the magistrates by answering questions with strange answers. She continuously also taunts Hester and the scarlet letter on her bosom. It is as if the ambiguity of her birth is correlated to the oddity of her behavior.
These facts make the reader wonder what are Pearl's true intentions behind her behavior: has she been sent from "beyond" to punish Hester? Is she, indeed, an elf-child? Only after the truth is finally known is that Pearl resumes a normal life.
Pearl was born out of wedlock by Hester. In the 16th Century, the Puritans strongly denounced child birth before marriage and considered it a sin. That is the reason that Hester wears a scarlet letter. Hester also lives away from the town to show that the Puritanical church denounces such behavior.