If Leonard Bernstein’s own 1971 recording of his Mass (yes, italics – it’s a “Theatre Piece for Singers, Players and Dancers”, not a setting of the liturgy) is Gospel, Marin Alsop is the latest disciple to evangelise Bernstein’s most ecstatic, charismatic and sanctified music. Compared to the intellectual fence-sitting and crackerbarrel mysticism that – since Holy Minimalism became the latest must-have lifestyle soundtrack – is every place, Bernstein’s relationship with God is dangerous, probing, transformational. There are those, of course, who proffer that Bernstein thought he was God, that’s why he could stand in defiance against Him. But, no – Mass reveals a man thirsting for faith but petrified of blind acceptance. Bernstein’s religion was muscular and intellectualised, and the experience of Mass expands, rather than contracts, the further you travel towards the essence of its cosmology. When Kent Nagano brought down the tablets of stone in 2003, frankly, he dropped some. Jerry Hadley sang the anchoring role of the Celebrant with obedient accuracy but lacked the lusty, unselfconscious mania with which Alan Titus sexed up Bernstein’s account. Released earlier this year, Randall Scarlata in Kristjan Järvi’s performance preached with soul and fervour: but Alsop’s Jubilant Sykes is the best of all possible Celebrants.

There can be few roles in contemporary music theatre that demand so many sides of a performer. The Celebrant is a near-constant presence on stage throughout the just-short-of-two- hour duration. He must disentangle music of gnarly complexity (“The Word of the Lord”), and bringing appropriate sincerity to writing that could slide towards doe-eyed naivety (“Simple Song”). “The Lord’s Prayer”, segueing into “I Go On”, needs an operatic sensibility, while the Celebrant must also swing like a hipster jazzer and declaim with authentic rockist swank.

And those are just the technical riders. Mass follows the Celebrant to the darkest place a proselytiser for faith can travel – from sneaking doubt towards a full-scale breakdown as, in Bernstein’s climactic scene, he trashes the altar and sends the sacraments scattering. Sykes brings an intensity that chills. In his joy is pain; in the agony of his crack-up is hope that does, indeed, ultimately blossom. His voice shakes with James Brown’s ecstasy, snarls with Janis Joplin-like indigence and projects through the labyrinth of Bernstein’s tricky melodic contours like any trained voice would. Sykes was born to play this part.

The stage action was Bernstein’s parable for 1970s America; an America fighting a controversial war, ravaged by political and racial conflict, and the assassination of anybody who was a force for good. To portray a society in freefall, Bernstein illuminates all its music. At the beginning vocal and percussive fragments leer at the audience from out of quadraphonic speakers like latter-day Ives, and musical modernity breaks out everywhere. An atonal oboe solo sounds like calculated blasphemy, stretching chromatic choral fragments leave singers grasping free-for-all notes in aleatoric freak-outs; tonality gets refracted through tone-rows and clusters. Over this shifting abstraction, Bernstein layers church music, blues, jazz, even a brief quote from Beethoven. This is our world now, Bernstein proclaims: no place for art that thinks it knows itself.

Just as the Celebrant flips comes the most remarkable passage of all – a funky 10-bar refrain of “Dona nobis pacem” which is reiterated deliriously as blues singers improvise added lines and, eventually, the orchestra is invited to holler above “anything from the entire musical literature”. Although she doesn’t drive things quite as far as Bernstein, Alsop ensures this passage pushes the Celebrant over the top and Sykes’s portrayal of the breakdown is moving and sensitive; the orchestral playing too, here and throughout, is lusty and unafraid to let go. Järvi’s handling of that same moment is more contained, and his tendency is to stress points of demarcation within Bernstein’s stylistic smorgasbord. Alsop is pacier, creating a dramatic slipstream that is powered relentlessly onwards by the awkward discontinuities and jagged narrative.

Even if this atheist cannot quite love the God-fearing D major affirmation of the final scene, as the Celebrant reconnects with his faith, it doesn’t matter. The journey – the process of discovery – counts for more. The haughty certainty of bad religious music is bad religion, worse music. Beethoven’s Credo from his Missa solemnis, Tippett’s A Child of Our Time and Bernd Alois Zimmermann’s Requiem for a Young Poet probe the terror of God. Bernstein’s Mass sits in that tradition: make our garden grow – go tell it on the mountain.