‘After death, if there is something, I hope for the possibility to visit any moment of humanity for eternity.’ I didn’t expect my conversation with French conductor Raphaël Pichon to touch on the eschatological, but if any piece of music in the Western canon was going to make us ponder the afterlife, of course it was going to be Bach’s B Minor Mass. ‘If for eternity you are able to visit like a ghost to get some answers, I would go back to the creation of the Messe de Nostre Dame by Machaut, and then, of course, the first performance of Bach’s St John Passion in Leipzig. But the first violinist in Dresden who faced that first bar of the B minor Mass: he must have been afraid, shocked or scandalised. Perhaps he thought it was a mistake!’ Pichon is referring to the opening ‘D’, which for the Paris-born countertenor turned conductor is less a note and more an imploration. He describes the D in the first violins, hovering above the stave, two octaves above middle C, as ‘frighteningly high … a scream uttered by all of humankind’.

Pichon believes that the opening four bars of the Mass, which ‘obsessed’ him for years, reference 18th-century performing traditions such as those in Dresden: ‘The start of a Mass was a moment of Italianate improvisation based on one, two, maximum three chords, where the players embellished a kind of cadenza before the counterpoint.’ He takes a cue from an often-overlooked detail: the marking of Molto adagio in the cello manuscript of the Dresden parts (in the other parts, it is simply marked Adagio). ‘It’s really slow. The marking means that it is slower than a heartbeat. If we’re talking in modern language, it’s in slow motion. And this creates so much tension, it’s an enlarged expression of despair. So there’s this sensation that it’s all of humanity begging for mercy. So, no, it’s not elegant, it’s not beautiful: it’s painful, desperate, terrible.’

Next year will mark two decades since Pichon founded his ensemble Pygmalion, and he notes how Bach has been with them since their very beginnings. The group first embarked on the Missae breves and then moved on to perform the cantatas, movements of which Bach recycled to make up a significant part of the Mass in B minor. ‘I think it was in 2013 that we first performed this Mass, and every three years we have had the chance to revisit it, touring it with different kinds of forces but almost always with people that I’ve been playing with for years. It’s a family story. And it’s so difficult to accept that now we have fixed it.’

For the recording, Pichon used a copy of the score that has also been with him since those beginnings. It’s delightfully tatty, and he takes pleasure in showing me its disintegrating spine, the sedimentary layers of red and blue pencil, and streaks of eraser. ‘I’m the kind of musician who annotates. I write a lot of things – words, phrasings, ideas – on my main score. So to record the piece was also to face what I wanted to keep. Sometimes there are details that I feel I’m so far from now. I needed to make sure that I’m not a prisoner to all these past experiences and that I continue to face it in a really fresh way – to read with the sensation of discovery. With unique pieces such as the B minor Mass, the details you continue to discover are endless: hidden voices, counterpoints, characters, harmonies, details of instrumentation. And to do this all the while with the same musicians … we had to make it like it was love at first sight, love at first time.’

It’s not difficult to see why these musicians have remained so loyal to Pygmalion: Pichon is utterly captivating. As we turn the pages of our respective copies to the ‘Domine Deus’ (which the conductor calls ‘one of the work’s most touching movements’), he leans in close. As he waves his hands, his movements seem to scent the air and it feels as if I am being conducted if not hypnotised.

‘There is something childlike about this movement in the most noble way. I could even be more precise; I have my favourite bar.’ Pichon points to bar 42 and his eyes light up in Willy Wonka wonderment. ‘Unisono, violins plus violas – the most simple expression of tenderness of this era; the harmonic sequence and its natural Italian dissonances, one voice plus the other, and on the top of that, just this choreographic gesture – a hand reaching from behind to touch your shoulders, coming from the strings – able to create the movement to refresh the second harmonic sequence. I cry when we are there. And the players know it perfectly, too.’ Pichon loves the fallibility of that moment. ‘For reasons I can’t explain, players forget to play there. There is this tiny electricity in the air. “Is this the right beat to play? Where? Oh no, it’s there.”’

Coincidentally, the ‘Domine Deus’ movement has lain at the heart of Bach studies; or more specifically, its first bar has brought controversy. Even in the 1850s, the rhythm in the flutes was known to be reverse-dotted – a flickering Scotch snap or Lombardic rhythm that would have been all the rage at Dresden’s fashionable court. Surprisingly, perhaps, Pichon conducts from the 1954 Neue Bach-Ausgabe edited by Friedrich Smend (he tells me it’s the seventh revised printing, from 2005), which famously ignores this detail captured in the manuscript of the first flute part, ironing out the rhythm to make even semiquavers. As the musicologist and conductor Joshua Rifkin writes, this and other details amount to ‘more than philological quibbles’: the Lombardic rhythm is evidence of Bach’s awareness of, if not interest in, the latest musical trends. Through his edition, Smend sought to construct an image of Bach as unswayed by changing styles and instead steadfast in his role as the traditional Lutheran cantor.

Pichon’s recording somewhat cheekily nods to this debate: we’re initially given Smend’s version, but patient listeners are rewarded with Scotch snaps when the material is recapitulated from bar 60. It’s perhaps emblematic of what Pichon thinks scholarship offers to performance, especially concerning the central debate of whether Bach conceived the B minor Mass as a unified whole: ‘It creates the opportunity to reconsider and reread the story of Bach and all the contexts he had to face. But at the same time, I don’t care. If we’re speaking about message, architecture, journey, it’s the story of the whole of humanity in two hours of music. So while I’m fascinated by all these musicological issues, it will not change the fact that the final result is a work of pure genius.’

Despite its hugeness, Pichon is seduced by the work’s moments of smallness and stillness. We discuss the transition from the ‘Confiteor’ to the ‘Et expecto’, and Pichon speaks in reverent tones. ‘It’s one of the only moments in Bach’s output where he opens a door of his intimacy that he ordinarily does not open. In the middle of something normally so monolithic, so solid, Credo (“I believe”), and in this expression of faith, to open this little door where there is doubt … We reach a no-go zone where we are blocked: there is no exit. It’s finished. But then, there’s a really small gap, just a tiny ray of light appearing from the sopranos – a bit afraid, hesitating, and then with the same words again. Blinded with sudden optimism, sudden light and hope, the word “expecto” is transformed – suddenly the meaning is not “I am waiting” for something, but “I hope” for something. So, suddenly, it’s “I believe” again.’ Spend an hour talking about Bach with Pichon, and you too will believe again.