There was a man called Guo Han in the Tang Dynasty(618-907).
One summer night, when the moon was very bright he suddenly saw a girl descending（下降） slowly from the sky. He observed the girl closely, and found that the dress she was wearing was seamless（无缝的） . He was puzzled, and asked why. The girl answered,"Heavenly clothes are not sewn with needle and thread."
This idiom is used metaphorically to indicate the flawless handling of things. It can also be used to indicate a perfectly written poem or other literary article.

传说古代太原人郭翰在夏夜里乘凉，见一个仙女从天上下来，她身穿白衣，美丽绝伦。她告诉他她名叫织女。郭翰仔细欣赏织女的衣裳浑然一体，竟看不出一丝线缝，好奇问织女。织女答道：“天衣本非针线为也。”
神话传说，仙女的衣服没有衣缝。比喻事物周密完善，找不出什么毛病。