The original words of this sentence are "the monarch is a rock, the concubine is a reed, the reed is like silk, and the rock does not turn." From Peacock Flying Southeast, the sentence means: You must be a rock, and I must be grass and reeds. Grass and reeds are as soft as silk, and rocks are not easy to transfer.
Stone: A thick and big stone. This is a metaphor of unswerving love faith.