There was a man named Guo Han during the Tang Dynasty (618-907). One bright summer night, he suddenly saw a girl descending slowly from the sky. Observing her closely, he noticed her dress was seamless. Puzzled, he asked her why. The girl replied, "Heavenly clothes are not sewn with needle and thread."
This idiom is used metaphorically to describe the flawless handling of matters. It can also refer to a perfectly crafted poem or piece of writing.