Chinul (1158 - 1210) was one of the first great masters of Korean Zen. He focused the tradition on meditation practice and established a foundation in the sutras for Zen teaching.
Chinul also introduced hwa-du practice (Chinese: hua-t'ou) as a primary training technique. This is the practice of holding a great question, such as "What is this?" throughout meditation and daily life.
Yet, for all his brilliant formalizing of Zen training, he kept his eyes clear about the nature of the teaching, as shown in this passage:
It is sad that people have been confused for so long. They do not understand that their own minds are Buddha and that their own natures are Dharma. They look for Dharma by searching out sages far away. They look for Buddha but do not observe their own minds.
If they aspire to Buddhahood while clinging to their opinion that Buddha is outside the mind and that Dharma is outside their own nature, then even if they burn their limbs and break their bones for a million kalpas to show their sincerity, even if they sit constantly and never lie down to sleep, write out sutras in their own blood, eat only one meal a day, and practice every austerity - it would be like trying to cook rice by boiling sand, and in the end they will only wear themselves out.