We chant the Heart Sutra after Zazen because the Heart Sutra is an expression and description of Zazen.
In the version we chant, the first sentence is usually translated “the Bodhisattva of compassion, practising the Perfection of Wisdom, clearly sees that the five skandhas are empty and thereby relieves all suffering”.
Chapter 2 of Shobogenzo is Dogen’s commentary on the Heart Sutra. The first sentence is his adaptation of that sentence, as follows: “Avalokiteshvara bodhisattva, while experiencing deeply the manifestation of prajna, clearly saw with the entire body that all five skandhas are empty” (Tanahashi translation).
In this adaptation Dogen is adding something and taking something away. What he’s adding is a reference to ‘the entire body’. What he’s taking away is the passage about relieving suffering.
The reference to ‘the entire body’ is to get us out of the idea that Zazen is a personal practice. The bodhisattva of compassion, Avalokiteshvara, is identical to the entire/ whole body’, that is, with everything, with all beings.
His removal of ‘and thereby relieves all suffering’ is intended to get us out of a process view, of Buddhism generally and Zazen in particular. Namely, the idea that we do something (Zazen) and in that doing of something we realise something (emptiness) and that realisation causes something—the relieving of suffering.
The sentence now isn’t a sequence, it’s a description.
We can tell that because we can move the parts around and still maintain the same meaning. For example, we could say “the Bodhisattva of emptiness, experiencing deeply the manifestation of compassion, clearly saw with the entire body that all five skandhas are prajna”.
And Dogen does go on to do exactly this, identifying the five skandhas as being five pieces of Prajna.
Although the point might appear to be obscure, that assertion of Zazen as being a universal practice is very important. It’s not us practising, it is all of creation practising with this body within the entire body of all beings.
That’s not a sequential process.
It’s not “I was a deluded human being, then I made an effort and now I’m enlightened”. It’s immediate —it’s not developmental. It’s not progressive.
We see the whole of creation as compassion or as emptiness or as wisdom.
And that seeing pivots us. These apparently distinct terms —-compassion, Prajna, Emptiness, the entire body, are all synonyms for that which we can live but not name, expressed differently and seen and felt differently.