A common criticism of the composer John Tavener was that his work was "easy listening", prime fodder for Classic FM and schmaltzy adverts. There can be no doubt that he had popular appeal - in 1992, his cello sonata The Protecting Veil topped the classical charts for months, and millions wept as his choral work Song for Athene was sung as Princess Diana's coffin was borne out of Westminster Abbey in 1997. His became the sound of a time: his setting of the William Blake poem "The Lamb" was sung at the Millennium Dome in the final moments of 1999. The diverse sources of the tributes paid to him since his death  demonstrate this – as well as fellow composers and musicians, the Prince of Wales has let it be known that he is "saddened" by his death. Tavener was famous in a way more usually associated with a pop star – he was even signed to The Beatles' Apple label early on in his career, and was nominated twice for the Mercury Prize.
Tavener, who has died at the age of 69 after struggling with ill health for much of his life, had another side to his work, though, that more rarely made it beyond the awareness of those who make, read, and write about classical music. His conversion to the Russian Orthodox Church in 1977 had a profound impact on his composing, as he moved away from the modernism of The Whale and Celtic Requiem and began importing ideas from Gregorian chant, Orthodox liturgical traditions and eastern harmonies. Always, he told the BBC in 2003 , he was trying to find "a music that already exists in the cosmos" or "the uncreated music of God".
Nowhere is Tavener's search for "the essence of God" more evident than in The Veil of the Temple, the seven-hour choral work he composed in 2003. It is vast and complex, and is comprised of eight cycles, each of which ascends in pitch and reworks themes and motifs from what has gone before. Snatches of melody, verses from St John's gospel, and rhythms from Hindu devotions weave in and out of the motets, chants and solos that make up the piece. Tavener himself likened it to a "gigantic prayer wheel", but there is so much more than just devotional music to this piece. As well as being intended as the accompaniment for a dusk-to-dawn vigil, it is a kind of oratorio, telling the story from the rending of the veil in the temple in Jerusalem as Jesus died on the cross to Mary Magdalene discovering the empty tomb, seeing the risen Christ, and perceiving that the veil between death and life has been lifted.
It's also a piece inspired by a particular building – the Temple Church in London, where it was first performed. As Tavener wrote in the sleeve notes when the recording was released, when the Knights Templar built their beautiful round church, they were seeking to recreate something of the Church of the Holy Sepulchre in Jerusalem for their own place of worship and burial. The Veil of the Temple imports this, giving the Knights a theme in Cycle 8 of surpassing beauty that evokes a great feeling of peace and permanence. Occasionally interspersed between the vocal harmonies, though, are discordant organ phrases and the melancholy tolling of bells, which is Tavener's reminder that all is not at peace in the place the Knights sought to found anew with their church – Jerusalem itself.
Setting its spiritual and historical resonances aside for a moment, The Veil of the Temple is also just brilliant music to get lost in. The layering of liturgical chant with the clean harmonies of the western church and the intricate rhythms and cadences of eastern traditions is breathtaking. It is also written on a scale we are rarely treated to these days - it requires more than one choir, soloists who have been trained in both orthodox psalm-singing and the Hindu Samaveda, a brass ensemble, a virtuoso organist, Tibetan horns, temple bowls, tubular bells and more. Tavener himself told the Guardian earlier this year  that he thought "the days of seven-hour pieces are gone" and that even he was writing in a more compressed language these days.
It is to my eternal regret that I didn't go to the premiere in 2003. A close friend who did describes an extraordinary atmosphere of tension and anticipation over the hours of music, as it built implacably towards its glorious climax, and the catharsis when the musicians arrived at Cycle 8's "Light of Christ" just as the light of dawn began to filter in through the windows of the Temple Church. Steven Poole, who recorded his experiences of the night for the Guardian , said he would be quite happy to hear "Mother of God" from Cycle 7 over and over again all night, and I agree with him - a few simple-sounding chords underneath Lermontov's beautiful words are capable of provoking an emotional response that even the crashes and squeals of the piece's climax can't emulate.
Tavener called The Veil of the Temple "the supreme achievement of my life and the most important work that I have ever composed". Listen to it: there can be no more fitting way to mark his passing.