His "MU" was a blow aimed at breaking or untying the attachment even at the teaching itself; the essence is non-attachment. All human troubles and sufferings, without exception, are due to attachment. Even attachment to the idea of non-attachment is the attachment. It transcends the relative world and gains the free and independent world of satori.
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Our life is always attached to the relative: the "is" and the "is not," "good" and "bad," "right" and "wrong". But life itself constantly changing: the condition of society changes, right and wrong changes. Every situation is different according to the time and place. Static concepts are not appropriate to life, but the concepts like faith, hope, and love are; because they grow and evolve.
The Tao is infinite, eternal. Why is it eternal? It was never born; thus it can never die. Why is it infinite? It has no desires for itself; thus it is present for all beings. The Master stays behind; that is why she is ahead. She is detached from all things; that is why she is one with them. Because she has let go of herself, she is perfectly fulfilled. Tao The Ching Chapter 7