The most important literature for Zen is the Prajnaparamita literature (Hannya Haramita 般若波羅蜜多). The Essence of Perfect Insight sūtra (Maka Hannya Haramita Shin gyõ 摩訶般若波羅蜜多心経) constitutes the very essence of the perfection of insight. Often simply referred to as the Heart sūtra, this sūtra is a dialogue between Kannon Bosatsu (觀音菩薩) and Śariputra (Sharihotsu 舎利弗), one of the Buddha's two chief disciples.

Kannon Bosatsu represents perfect insight or transcendental wisdom. Śariputra was famous for his worldly wisdom, so the sūtra is actually a discourse between the more intellectual type of wisdom represented by Śariputra and the perfect transcendental insight or perfect wisdom represented by Kannon Bosatsu.

In the dialogue of the sūtra, Śariputra doesn't answer back. This points to the intellect having reached perfect insight, transcending itself, representing intellectual understanding in the process of being transformed into spiritual insight.

In the sūtra, Kannon Bosatsu makes six great statements to Śariputra; statements which shatter all Śariputra's prejudices and serve to drop all boundaries. They destroy the lower intellectual wisdom and reveal the higher wisdom, the perfect wisdom or insight.

The most important statement made in the sūtra is that a Bodhisattva (Bosatsu 菩薩) gains enlightenment, becomes a Buddha, only by relying on perfect insight. There is no other way. One can't become enlightened without developing perfect insight. Buddhahood comes only through perfect insight.

At the end of the sūtra is a mantra (shingon 真言), a device for deepening ones thought. The entire sūtra is condensed within this mantra. To recite this mantra by itself, omitting the text of the sūtra itself, is the practice of non-discriminating mind. The complete understanding of the sūtra is encapsulated within the mantra.

THE ESSENCE OF PERFECT INSIGHT SŪTRA

Serious contemplation of this mantra together with regular and deep meditation practice is designed to enable us to penetrate our illusions about the nature of reality which is perpetuated by our inaccurate perception of the world and ourselves.

Insight has to be gained into the impermanent, unsatisfactory and essence-less nature of all conditioned phenomena, of everything mental and physical. Insight develops slowly and gradually through the careful process of observation, investigation and analysis of phenomena until we achieve perfect insight - the ultimate nature of all things revealed - the nature of emptiness.

It is just through investigation and wise consideration of phenomena that insight into their ultimate nature develops. Carefully directed thought, while sitting in meditation, is a vital tool for the rooting out of all our ignorance. As we increase our understanding and wisdom through meditative investigation, we decrease our ignorance, and as ignorance diminishes we are loosening the bondage of our suffering and becoming more and more free of craving.

To practice the teachings correctly, we should endeavour to liberate our thoughts from delusion; the attainment and practice of truth are the means to the attainment of perfect insight (hannya 般若).