Figurative language is a literary device in which you use words with non-literal meaning in order to achieve a literary effect on the audience. There are several types of figurative language such as metaphor, personification, similes or hyperbole.
In this case, the author uses sweetness and light non-literally in order to express that before Mistress Hutchinson had arrived, he was happy and joyful. Mistress Hutchinson's arrival does not mean literally chaos, but it means that it brought changes to the narrator's life and he does not like it. Mistress Hutchinson becomes the personification of chaos for the narrator.
