After zazen when we chant the Heart Sutra we are chanting the short condensed version – heart/essence – of the massively longer Great Real Wisdom Perfection Sutras (an early Mahayana work begun around the 1st Century). The Japanese title is Maka hannya haramita shin gyo. What we chant is the most common version chanted in China and Japan, translated by Xuanzang (Jp: Genjo) into 260 Chinese characters.
The first lines in our chant copy is an introduction to the sutra and expresses our zazen practice.
In the title –
Maka is vast or great. Hannya is prajna or intuition or wisdom, beyond what can be intellectually discriminated (the sutra is about this, encourages us to investigate the way things really are, to explore our experience and existence), haramita is paramita or perfection, shin is heart-mind but in this case essence, gyo is sutra, which as a kanji character expresses spaciousness (eg can also mean longitude).
The start of the Hannya Shingyo –
Kanjizai bosatsu – Kannon/ Guanyin/ Avalokitesvara Bodhisattva – gyo jin hannya ha ra mitta ji – through (or going/ impulse) the deep prajna paramita practice time – sho ken go on kai ku – sees with illumination the five skandhas empty – dou issai ku yaku – with a single cut saves beings from pain/ suffering.
So zazen practice is dwelling profoundly in and dynamically enacting prajna.