Pearl and the brook in Chapter 16 are very similar. Pearl notices the brook when sent off so her mother and Dimmesdale can have some privacy to talk about Chillingworth. Pearl feels that the brook is sad and decides to try to cheer it up. Pearl has much in common wit this brook, though - they both come from something mysterious and unknown, covered in real and metaphorical shadows. They also are more free than is revealed by the naked eye - they don't have to follow the rules. The brook may flow, unrestricted, wherever it pleases. The same is true for Pearl. She may reach her goals by whatever means are made available to her. She seeks the truth by asking the tough questions. She knows what she is, though, and knows where she came from even if most everyone else does not.
She and the brook are what Hawthorne considered to be ideal - free from the restrictions of societal expectation. Free to feel what they feel and think about it later.
Pearl, the incarnation of a natural love between a man and a woman, is akin to the brook and the forest. She is a product of nature, unlike her mother and the minister, who represent the Puritan society and its restrictions.
The brook and other aspects of nature are often exemplary of pathetic fallacy, as in Chapter 16. For instance, Pearl asks, " What does this sad little brook say, mother?" And her mother answers,
"If thous hadst a sorrow of thine own, the brook might tell thee of it...even as it is telling me of mine."
Also, Pearl resembles the brook because "the current of her life gushed from a well-spring as mysterious," and this current flows through places heavily "shadowed with gloom."
In Hawthorne's narrative, the forest primeval is representative of nature that is free of restrictions and laws. Pearl is also free, and she is in harmony with nature, being bound by no social or religious restrictions. In the brook in which she sees her reflection, there is Hawthorne's symbolism for the imagination.[Often he uses a mirror as this symbol.] So, this is why Pearl who has been listening to and gazing into the brook asks her mother the imaginative question of why the minister who approaches holds his hand over his heart. Also, because the brook represents nature that is not bound by restrictions, Pearl refuses to cross it until her mother, who is part of the Puritan society, replaces the scarlet A upon her bosom.