What is the origin of the idiom "sweetness and light" and when to use it?

The idiom "sweetness and light" is often used to refer to a state of peace, harmony, or enlightenment. It originates from a phrase used by the English essayist and critic Matthew Arnold in the 19th century, in his essay titled "Culture and Anarchy" (1869). Arnold used "sweetness and light" to describe the desirable outcome of a society that pursues intellectual and moral improvement.