相敬如宾

During the Spring and Autumn Period (770-476 BC), there was a high official in the State of Jin. He once saw a farmer working in the field and his wife bringing his lunch to him in a very respectful manner. He showed great interest in the matter. He took the farmer back to Jin with him, and said to the King of Jin, "Respect is a demonstration of virtue. If one is respectful, he must be virtuous. We should educate our people with virtue." But the King asked, "His father is guilty, is it wise to do so?" He replied, "Guan Zhong had been enemy to the Duke Huan of Qi, but the duke appointed Guan Zhong prime minister and finally accomplished his hegemony. Shun exiled Gun but promoted his son Yu. You just make use of his strong points." At last, Duke Wen took his advice and put the farmer in an important position.

Later, this idiom means a couple treats each other with respect like guests.