Hui-chung answered, "There is a difference when one is deluded. However, if one is enlightened, there is no difference."
The novice further asked, "The sutra states that the Buddha-nature is permanent whereas the mind is impermanent; why do you say that there is no difference?"
Master Hui-chung patiently replied, "You only understand this by the characters and not by its implication. For instance, when the temperature drops to the freezing point, water will freeze into ice, and when the temperature rises, ice will melt into water. Similarly, when one is deluded, one's self-nature will turn into the mind, and the mind will turn into self-nature when one becomes enlightened. The mind and self-nature are originally the same. The distinction depends on whether one is deluded or enlightened."
FInally, the novice understood.