kirtu wrote:I haven't read the McLeod book or the Mu Soeng book but the others are essentially pointing to or teaching the Prajnaparamita (I was going to say they are essentially the same).
Since the Heart Sutra is brief, one can explain it in as many different ways as emptiness can be explained in different ways. Same with the concept of prajnaparamita. You can go with Madhyamaka, Yogacara, Tiantai, Huayan, Chan, Tantra, Mahamudra, or something new.
For instance, Ven. Seung Sahn distinguished three forms of Zen (theoretical, tathagata, patriarchal) based only on "form is emptiness, emptiness is form" (Compass of Zen, p. 229f). Dushun's Mirror of the Mysteries of the Universe of the Huayan (tr. by Cleary in Entry Into the Inconceivable) sets up the whole discussion based on a fourfold relationship between form and emptiness. There is also a Heart Sutra commentary by Fazang translated in Francis H. Cook's "Mahayana Buddhist Meditation" that follows Huayan exegesis and differentiates three meanings of the relationship between form and emptiness (mutual opposition, not mutual opposition, mutual creativity), then gives the four meanings of true emptiness, after which he lists another fourfold relation from the viewpoint of form, following in essence Dushun's analysis. Shunryu Suzuki, in Zen Mind, Beginner's mind (p. 25f) makes difference only between two views of form and emptiness, where the view of "form is emptiness, emptiness is form" is a dualistic view. These were only Buddhist interpretations. But if we look into other sources, like "The Eye Aware: Zen Lessons for Christians" by Jeroen Witkam, we may find even more interesting explanations. That's why I say that studying the Heart Sutra is far from simple and straightforward.Seung Sahn: Form is Emptiness, part 1
(video)Seung Sahn: Form is Emptiness, part 2
Finally, here's a bit of Dogen (SBGZ: Bussho), just for its nice wording.
(tr. C. Bielefeldt):This “emptiness” is not the “emptiness” of “form is itself emptiness.” “Form is itself emptiness” does not mean that “form” is forced into “emptiness”; it does not mean that “emptiness” has been divided up to author “form”: it is the “emptiness” of “emptiness is emptiness.” The “emptiness” of “emptiness is emptiness” is “a single stone in space.”
(tr. Nishijima & Cross):This emptiness is beyond the emptiness of “matter is just emptiness.” [At the same time,] “matter is just emptiness” describes neither matter being forcibly made into emptiness nor emptiness being divided up to produce matter. It may describe emptiness in which emptiness is just emptiness. “Emptiness in which emptiness is just emptiness” describes “one stone in space.”