Roderic Dunnett writes:

THE death of Sir John Tavener at the still early age of 69 is a loss not just to British music, but to the arts worldwide; for this idiosyncratic composer had a reputation akin to that of the Estonian Arvo Pärt, in redefining the sounds of church and religious music and giving them a new, direct, and optimistic impact.

Tavener achieved this by returning to music's roots to seek a new purity and simplicity, make it integral to how sacred texts are approached, and achieve an almost mesmerising power of communication, accessible to an ever widening audience. His erstwhile Orthodox mentor - the late Mother Thekla, of the Greek Orthodox Monastery of the Assumption, Normanby, in North Yorkshire - pertinently observed: "Perhaps the reason why his music appeals to so many non-believers is that it reminds them of a time when they did believe in something."

His death is a loss to Tavener's family, too; for he had that joy special to older parents of fathering a son in later life, who could be seen cavorting around and attending intently at the recent celebration of Tavener's works at Manchester's Bridgewater Hall. The bond between the two was patent and precious; his passing is going to be a hard loss to understand and bear.

The impact of Tavener's music, fired by the long-breathed chants of the Eastern Orthodox Church, which he embraced in middle life (Russian Orthodoxy from 1977, later inclining more to Greek), has rarely been more obvious than when he wrote the 50-minute orchestral piece The Protecting Veil for the cellist Steven Isserlis, a work delivered with such passion and aching beauty that it could not fail to stir hearts of any persuasion. That initial recording has just been reissued by the BBC Music Magazine.

There was also the astonishing All-Night Vigil: The Veil of the Temple, which he penned for performance in 2003 at the Temple Church, London. The venue reminds us that Tavener was interested not just in various brands of Christianity, but in syncretic aspects of religion - the fact that, say, Coptic Christianity, Islam, Hinduism, and Buddhism all have related cultural backgrounds and content, and that each has something to say to the others.

Many listeners will know him for his famous short anthems, often included in Anglican services. His setting of William Blake's "The Lamb" (he also set "The Tyger") is one candidate for the best-known church anthem of the 20th century; yet it also draws attention to a secular content in Tavener's output - Sappho: Lyrical Fragments, for instance, Sixteen Haiku of Seferis; or The Uncreated Eros, which show his love for things Greek reaching beyond Orthodoxy, and even encompassing the erotic; and his string quartets, although even they acquire religious captions, such as the third, Diodia.

Or there are, for another example, his exquisite song settings of the profoundly wise dissident Russian poet Anna Akhmatova (1889-1966). He set her masterpiece, the 1930s poem cycle Requiem, which bears witness to the horrors of the Stalin's purges.

Funeral Ikos, Akathist of Thanksgiving, the vital Today the Virgin, and Song for Athene, famously reworked for the funeral of Diana, Princess of Wales in 1997, and To a Child Dancing before the Wind (charmingly echoing titles like Debussy's The Girl with the Flaxen Hair) are among other works high in a wider public esteem. For some of that we owe a debt to Martin Neary, who, as organist of Winchester Cathedral and then of Westminster Abbey, did much to further Tavener's cause, engaging with his boys the highest possible musical standards.

The works all, or nearly all, have a key characteristic. As others drew on plainsong, and fragments of it, Tavener took from his Orthodox affiliation the building blocks - simple 1-2-3-4 patterns, from the more extended Byzantine tones, whence he could craft small and large works alike from tiny scintillae of music. This is the practice of great composers throughout the ages, from Machaut and the 15th century to Bach, Brahms and Schoenberg. His ability to sculpt with his material is what made Tavener a great composer.

Alongside Hymn to the Holy Spirit and Hymn of the Unwaning Light, Hymn for the Dormition of the Mother of God provides evidence of Tavener's Marian devotion, one of many aspects of his faith which were intensified by his close relationship with Mother Thekla. Another was his absorption with the spiritual nobility of the fallen woman, as witnessed in his important opera Mary of Egypt, which first drew him into Mother Thekla's orbit, and yet latterly helped to sunder their relationship. The Great Canon of St Andrew of Crete was another work that reflected their discussions and often shared thinking. Thérèse, based on the life of St Thérèse of Lisieux, was not an immediate success. His opera A Gentle Spirit was based on a dark and troubling Dostoevsky story.

Tavener lived just long enough to see a revival of interest in his early works. As a music scholar at Highgate School, where he was a contemporary of John Rutter, he was a concerto-standard pianist, and - the son of a Hampstead organist - he loved the organ especially: like his father, he found a Presbyterian church, St John's, Kensington, to serve as organist.

Tavener and Rutter greedily absorbed everything that they could get their hands on: that is what young composers, and young geniuses, do. The Magic Flute at Glyndebourne fired him to music as drama; Stravinsky's Canticum Sacrum woke him up to contemporary music. Both helped to give him a calling. He pursued it at the Royal Academy of Music under Lennox Berkeley's tuition.

Indeed, such early influences surely fed into his first larger works. The Whale (Proms, 1968) is a masterpiece of merging styles, amazing from a young composer; his Celtic Requiem, a stupendous sequence incorporating children's voices, suggests Stockhausen's groundbreaking Der Gesang der Jünglinge (Song of the Children). A chance encounter with Ringo Starr and then Paul McCartney led to the recording of both works - each dazzling - on the Beatles' Apple Label.

Tavener was a bit of a star himself: often genuine, unashamedly intense, occasionally posey. But his love for things Russian, and Greek, things pure and things erotic, the sanctified and the fallen, and yes, for people and young people, made him both a polymath and rather special. We need Taveners, or something of Tavener, in our lives. The loss of this one, whose 70th birthday we were due to celebrate two months hence, will leave a hole.