Soaphead is the novel's quintessential dirty old man. He internalizes his family's obsession with whiteness but takes it in a surprisingly pedophilic direction. Just as Pecola associates whiteness with purity and beauty, Soaphead associates whiteness with purity and the innocence of children. It's no accident that when he speaks of young girls he has molested in the past, he refers to their "white laughter."
It seems important that the most religious character in the novel is also one of the most immoral, stuffy, and unlikable characters. Where other characters, like Pauline and Cholly, receive some kind of redemption – either through their back-stories or the sympathy of the narrator – Soaphead receives neither.