Wŏnhyo (Weonhyo, meaning ‘dawn light’, 617–686) is the most cherished figure in Korean Buddhist tradition. He was born during the period of the Three Kingdoms in Silla which absorbed the other two (Koguryŏ and Paekche) by 668. Buddhism, which became Silla's state religion in 527, was understood at the court as a force for developing the country and achieving unification. At large it was characterised by a variety of sects and schools of thought brought from China. According to one tradition Wŏnhyo became a monk while still a boy, other sources place the event in the 29th year of his life, but maybe this was the year of his full ordination. He is reported to have led an eccentric and itinerant life throughout. At one time (659) he had an affair with, or was temporarily married to, a widowed princess (their son, Sŏl Ch'ong, became a Confucian scholar and is reported to have had a hand in adapting Chinese characters for writing Korean words). This affair became a popular romance, eventually elaborated even into a modern novel (1940) by Yi Kwangsu.

Wŏnhyo studied under different teachers who had been trained in China and knew most of the scriptures they brought to Korea, but he never made it to China himself. A tale related in the Sŏn (Seon, Zen) type biographical work Records of Fingers Pointing to the Moon by Qu Ruji (1602) describes his two attempts to go there in the company of Ŭisang (625–702): in 650 they were detained when travelling through Koguryŏ (Goguryeo) territory as spies for Silla, but managed to escape back to Silla. When Silla conquered Paekche (Baegje) in 660, it gained access to safe sea ports. On the way to them in 661 the two were caught in a storm and took refuge in what they thought was a cave. Wŏnhyo quenched his thirst from a bowl full of rain water which he found in the darkness, but in the morning he saw that they slept in a tomb and the bowl was a skull. The storm continued raging and they had to stay put another night deeming themselves haunted by ghosts. Pondering over the satisfaction in quenching his thirst and the revulsion he felt when he saw the skull he had drunk from as well as the peace of mind when he thought he slept in a cave and the sense of being haunted by ghosts the next night, Wŏnhyo realised that all experiences were in the mind – and so was the final truth. When this truth was realised, external projections could not abolish it, even though they continued. Wŏnhyo then saw no point in continuing his journey (while Ŭisang went on, returned from China in 670 and founded the Hwaŏm [Hwaeom] school based on Aavataṁ saka Sūtra or ‘Garland of Discourses’).

Wŏnhyo's realisation of inner calm undisturbed by external projections is probably the source of his ability to reconcile his boisterous lifestyle, in which he continued, with extensive scholarship and with his way of spreading the message of the Buddhist goal of salvation to the masses by popular means which included poetry, music and dance. This gave Korean Buddhism a lasting flavour well illustrated by annual festivals in honour of Wŏnhyo still held in Punhwangsa (Bunhwangsa), a temple site near the old Silla capital Kyŏngju (Gyeongju).

Wŏnhyo's learning is attested by 23 preserved works of 86 he is reputed to have written, a result of not only prolific study of scriptures, but also of countless discussions with teachers of all sects and schools he could encounter, besides his original thinking and insights. True to his understanding that different external teachings, although valid in their own way, are the mind's projections as any other phenomena which find their fulfilment and reconciliation in internal realisation of final truth, he worked all his life for the reconciliation of all sectarian teachings and schools of thought. Nearest to his understanding of the Buddhadharma was the Chinese Tiantai (T'ien T'ai) school based on the Lotus Sūtra with its teaching that all things harboured at bottom the Buddha-nature. He therefore propagated its Korean form Ch'ŏnt'ae (Jeondae) which later brought into its fold Hwaŏm and Sŏn during the Koryŏ (Goryeo, 918–1392) period. When Sŏn reconstituted itself as Chogye (Jogye) school during the Chosŏn (Joseon, 1392–1910) period, it nevertheless retained under the influence of Ch'ŏnt'ae teachings a distinctive character which differentiates it from Chinese and Japanese varieties of Zen. For the salvation of masses Wŏnhyo upheld also the teachings of the Pure Land school; he regarded the mundane land and the Pure Land as correlative projections of the mind. It is hard to find a section of Korean Buddhism where some element of Wŏnhyo's influence cannot be traced. He is regarded as the greatest Buddhist thinker in Korea and acquired a great reputation also in China and Japan. When his Exposition of the Vajrasamādhi-Sūtra, which was probably his last work, was brought to China, it was given an honorary title lun, i.e. śāstra, indicating that it was on a par with traditional Buddhist scriptures brought from India.

Vajrasamādhi Sūtra or ‘Discourse on Diamond Absorption’ (rendered by Buswell ‘Book of Adamantine Absorption’), is a work regarded generally as originated in Ch'an (Chan, Zen) school in China; but Buswell, who provided its translation in his earlier book The Formation of Ch'an Ideology in China and Korea (Princeton, 1989), argues in it that it was composed in Korea around 680–685 by a person named Pŏmnang, but the question of authorship can hardly be regarded as settled. In any case, the intention of the compiler clearly was to make it seem as if it came from India by giving it the Sanskritised title and using Sanskrit terminology when describing the nature of consciousness and states of mind in meditative absorptions. The main purpose of the Vajrasamādhi Sūtra is to show a way to restoring ‘original enlightenment’ which, in Buswell's words, is in East Asian Buddhism innate to the mind and inherently accessible to all. He credits Wŏnhyo with being the first who saw outlined in this sūtra a way of cultivating original enlightenment systematically. The fact that beings are not aware of their inchoate buddhahood (tathāgatagarbha) is due to adventitious defilements. Being extrinsic, defilements cannot touch the intrinsic luminosity of the mind. All beings are therefore enlightened, even if they do not know it. In a note Buswell rightly invokes the quotation from the Aṅ guttara-nikāya 1.10 about the luminosity of the mind (prabhassara citta) and the adventitious defilements to show the early Buddhist source for the Mahāyāna elaboration of the doctrine of original enlightenment. In his initial study as Part I of this book he then explains how Wŏnhyo in his exposition of the Vajrasamādhi Sūtra outlines six specific stages of contemplation culminating in the ‘single-taste’ contemplation which amounts to experiencing the tathāgatagarbha or to realising the original enlightenment. The single-taste designation of this achievement is again a reference to an early Buddhist passage – in Cullavagga ix.14 – where the Buddha is reported as saying: “As the vast ocean . . . is suffused with a single taste, the taste of salt, so too . . . is my teaching and discipline suffused with a single taste, the taste of liberation”.

It would be of course helpful to have read the Buswell's translation of the Vajrasamādhi Sūtra in his earlier book before embarking on the study of the present one, but Wŏnhyo quotes in his Exposition a number of passages from the Vajrasamādhi Sūtra in which Buswell made some new minor revisions. This book can therefore stand on its own as a self-contained study. In truth, it is not just a translation with an Introduction, but a scholarly work in its own right. Buswell's introductory study elucidates on 43 pages many of the topics discussed in the Exposition as well as the circumstances under which it was written. The translation of the Exposition is annotated and provided with headings for different portions of the text, named parts, subparts, sections, subsections, divisions and subdivisions. The book is a worthy first volume of the mammoth undertaking of publishing all works by Wŏnhyo, a truly towering figure in Korean Buddhism.