Buddha-nature as a pure potential
is fully indestructible,
while any defiled nature is fully destructible.
At the cremation of a dead monk, Hengchuan said: “Each and every one of you has a bit of wondrous, illuminated, true nature. When the fire at the end of the age sweeps through and the whole world is destroyed, this [Buddha-]nature is not destroyed. Reading scriptures, sitting in meditation, opening up the robe [to relax], extending the bowl, benefiting people and participating in communal labor, being born and dying, movements and actions – all of this is reality-nature.
“You don’t know where it is because of a moment of being deluded by falsity, of turning your backs on enlightenment and joining with the dusts [i.e. Spurning your own inherent potential for nondualistic direct perception, and becoming absorbed instead into attachments to the sensory world.] You don’t know where it’s at, so I have pointed it out for you.
“Retreat! Retreat! A fire-snake is coming to pierce your skulls!” Then Hengchuan threw down the torch [and lit the pyre]. [A fire-snake represents the flames of the funeral pyre, hence the inevitability of death.]