Teachings of the Northern school
From the few records remaining of the Northern school it appears to have been faithful to the pragmatic practices planted by Daoxin and Hongren, including chanting, sutra study and reciting the Buddhist precepts. It was, in fact, just these practices that facilitated Zen's access into popular Chinese society. In addition to the emphasis on meditation practice and traditional Buddhist morality and discipline, the Northern school stressed study of key sutras as guides to understanding the mind.
For Shenxiu and the Northern school, Buddhism can be summed up by the doctrines of sila, prajna and dhyana (moral discipline, wisdom and recollection and peace). These represent the three stages of gradual enlightenment: sila, the abstention from evil; prajna, the pursuing of good; dhyana, the purification of one's mind.
The Northern school of Shenxiu had preached that the road to enlightenment must be traversed "step by step," that there were in fact two stages of the mind — the first being a "false mind" which perceives the world erroneously in dualities and the second a "true mind" which is pure and transcends all discriminations and dualities, perceiving the world simply as a unity.
The false mind is the mind clouded by "impurities." Remember Shenxiu's poem:
Our body is the Bodhi-tree
And our mind a mirror bright.
Carefully we clean them hour by hour
And let no dust alight.
Our pure, original (and universal) mind is mirror-like, with the potential to reflect the whole universe. But attachment and delusion—the dust on the mirror—obscure our minds. We proceed from the "false mind" to the "true mind" step by step, through the suppression of erroneous thought, processes by the practice of dhyana or meditation, in which the mind and the senses slowly reach a state of absolute quietude.