The central idea of this excerpt is to convey that aside from Pearl's beauty and brilliant, characteristically, Pearl will end up like Hester as said Pearl is "a young child's disposition" implying her characters will be an inherited from her mother, Hester. Also, as stated Pearl is "amenable to rules," it portrays a similar character to Hester, where Hester is also amenable to rules.
The central idea that Howard is trying to convey is