WHEN the now world-renowned Scottish composer James MacMillan composed one of his most celebrated early works, Seven Last Words from the Cross, he already had a cluster of small anthems to his credit.

But MacMillan’s fervent Christian belief, which would lead him for many years to conduct a church choir in Glasgow, was only just beginning to reveal itself in its full colours. Since the mid-1990s, he has composed a wealth of sacred choral pieces, some liturgical, and all rich in imagination, profound in their treatment of text, invariably original in design and concept, and roots, often, in Celtic chant — which is characterised by decorations and melismata that evoke a yearning feeling markedly individual and personal to this endlessly questing composer.

The marriage of passionate assertion and pained lament can be heard all through MacMillan’s Miserere, one of the two works newly introduced to the Barbican Hall in London, with aching, tender singing by The Sixteen, under their conductor Harry Christophers. That work, an astonishing weaving together of contemporary counterpoint, is in intensity perhaps the most substantial of those on The Sixteen’s recent recording devoted entirely to MacMillan’s sacred music (CORO 16096).

One reviewer stated (of “O bone Jesu”): “I can hardly imagine the composer will ever hear the work sung better than this.” This might apply equally to MacMillan’s brand-new work, a 50-minute Stabat Mater, which on its first hearing marked itself out as another milestone in his oeuvre: as powerfully compelling as his settings of the St John and St Luke Passions, massive works with a huge spiritual impact and such variety, energy, and contrast as to move as powerfully as a performance of Bach’s Passions.

In presenting the Stabat Mater as such a substantial work — in accordance with the aspirations of the Genesis Foundation, which has commissioned other notable MacMillan’s works for première by The Sixteen — the composer has embarked on a journey that, rather than merely evince the tenderness and compassion of the grieving Mary, subtly explores a host of other aspects of Jacopone’s 13th-century hymn text. MacMillan is not afraid to introduce fierce resentment, a sense of threat, an acute feeling of isolation, moments when the different lower voices engage in violent combat, and searing, scaring onslaughts (“et flagellis subditum”) to emphasise, aptly in certain stanzas, the bitter anguish of the poem as much as the mother’s tender cherishing.

The very start, with strings opening up below solo violin (the Britten Sinfonia’s remarkable leader, Thomas Gould), from violas and second violins to periodically ominous double basses, produced a full-string effect of close affinity with, and as bracing as, Witold Lutoslawski’s Concerto for Orchestra. The impact was stunning. A soprano was the first soloist (the pleasing “O quam tristis”), but even more striking were passages (“Fac ut ardeat”) where The Sixteen’s utterly superb tenors, solo or in duet or even sextet, produced a sound not unlike a muezzin calling from the minaret.

One extraordinarily appealing feature in this work, first performed on the feast day of St Teresa of Ávila, was how MacMillan by his ingenuity managed to prise from a string orchestra sounds that resembled woodwind or elements of soft percussion (for instance, heralding the focal stanza culminating in “dum emisit spiritum”). Another was the use of string staccato or semi-staccato — at times in deliberate conflict with other parts of the orchestra, to achieve added urgency and momentum.

Often it was in the instrumental interludes, some short but some substantial, between stanzas that the freshness and often daring of MacMillan’s musical thinking came through strongly. At one point, before “Virgo virginum”, the strings fluttered and took off with the vividness of a flock of birds.

Repetition, a crucial feature of effective choral writing, was plangently evident at “Sancta mater, istud agas”, where the start of one section, already dwelt on obsessively, was revived at the close: a forceful assertion, made a vital highlight by the composer.

But in other passages, notably “fac, ut tecum lugeam”, and — perhaps surprisingly — in the descending men’s-voice section, virtually a ritualistic wail, “Flammis ne urar”, which suddenly opens into a burst of pure tonal excitement, “per te Virgo, sim defensus”, there are moments of intense mystery and expectation, something that applies also at the close to the pianissimo whisper “Quando corpus morietur”. Near the end, a sublime melody for the cellos, yielding to an exquisite violin solo countered by nervous upper strings, made way for the repeated Amens. The effect, as so often in this brave new work, was magical.

The performance by The Sixteen, who were so beautifully attuned to MacMillan’s sacred output, could scarcely have been bettered. So, too, the curtain-raiser: the London première of a further piece, Seven Angels, featuring soloists, harp, and the haunting Jewish shofar, sung at St Giles’s, Cripplegate, by the choir Ex Cathedra, under Jeffrey Skidmore. This was a feast day of MacMillan’s music, and one could not have asked for more entrancing performances from all the forces concerned.