Yet Bach, ever pragmatic, found ways round these obstacles. For his St John Passion of 1724, he supplanted the paraphrased sections of the libretto from the popular Brockes Passion (a 1712 work by Barthold Heinrich Brockes) with the Gospel texts on which they were based. For the St Matthew Passion, he persuaded his regular collaborator, the Leipzig poet Picander, to build on his recent publication of poetic Erbauliche Gedanken auf den Grünen Donnerstag und Charfreytag (‘Edifying Thoughts on Maundy Thursday and Good Friday’) by adding more free verse suitable for use alongside Gospel texts. Picander duly created a libretto using Chapters 26 and 27 of St Matthew’s Gospel, as well as his own poetic meditations on the subject. Whereas the St John Passion uses texts from different sources, a single author overseeing the libretto for the St Matthew Passion lends it a particular coherence and flow.

As for the embargo on opera, Bach brought operatic elements into the St Matthew Passion by the back door, so that while the liturgical purpose of the work is ever-present in its pacing, rhetoric and tone, there are many innovative and daring stylistic elements that might have suggested associations with a world outside the walls of the church. Bach employed Italianate operatic styles, wide-ranging harmonic and key sequences, varied scoring and timbre, and dynamic extremes. The unusual key sequences, which can seem surprising, even disjointed, were partly a product of the dramatic structure, and partly conceived to jolt listeners into an awareness of the extraordinary nature of the events unfolding.

One of the most striking and ambitious features of the St Matthew Passion is Bach’s use of the double chorus. For the original 1727 version, he was writing for the two organ lofts of the Thomaskirche (similar in principle, if less grand, to the antiphonal effect created by two choirs in different balconies in St Mark’s Basilica in Venice, an influential feature of the Italian early Baroque). The first chorus and orchestra performed from the larger organ loft, with the second chorus and orchestra situated in the smaller organ loft, limiting the number of performers that could be involved. In the revised version of 1736, Bach augmented his forces, accentuating the contrasts between these two groups: both have soloists and chorus, strings and continuo including organ, and woodwinds including transverse flutes – prominent in the first alto solo – oboes and oboes d’amore, plus two oboes da caccia joining the first group.

The Thomaskirche’s ‘swallow’s nest’ organ (a decaying instrument that had to be demolished in 1740) was used to emphasise the ‘cantus firmus’ of the opening and closing choruses of Part I. There are two main parts to the St Matthew Passion, following the crucial moments of the Gospel narrative: preparation, Gethsemane and the arrest, Caiaphas, Pilate, Christ’s crucifixion; and, finally, burial and farewell. At the end of each scene there is a commentary on, or response to, the action from either chorus or protagonist, set to Picander’s poetic meditations. These vivid pieces form the core of the work, providing moments of contemplation or interpretation in a manner that would have made sense to a congregation used to similar structures in Lutheran services.