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."
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。"
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.
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。