This short text sums up well Bodhidharma's teachings, explaining in brief the principle (true nature) and the function (practice) of zen: THE ESSENCE OF MAHAYANA PRACTICE (with Annotation)
"There is no such thing as the real mind. Ridding yourself of delusion: that's the real mind."
(Sheng-yen: Getting the Buddha Mind, p 73)
“Don’t rashly seek the true Buddha;
True Buddha can’t be found.
Does marvelous nature and spirit
Need tempering or refinement?
Mind is this mind carefree;
This face, the face at birth."
(Nanyue Mingzan: Enjoying the Way, tr. Jeff Shore; T51n2076, p461b24-26)