Christmas Oratorio, AAM, Egarr, Barbican

Relatively recent tweaks to the abundant London concert scene have resulted in top-end events right up to Christmas. We have in part to thank the seasonal festival at St John’s Smith Square, postponing the Orchestra of the Age of Enlightenment’s holidays, putting them together with superb soloists and choirs, and serving up major Handel and Bach. One snag: their Christmas Oratorio when I last went to hear it turned out to be only four cantatas out of the sequence of six.

You’d have to pay two period-instrument horn players if you included Part Four – the OAE didn’t – and yet as Richard Egarr’s absolutely complete performance with the Academy of Ancient Music last night proved, the dark velvet sound of those horns, superbly played by Gavin Edwards and David Bentley (pictured left), along with the Oratorio’s most introspective magic made this the very heart and soul of the work. Not as far as the plot of the Christmas story goes; all that happens is the naming of Jesus at his circumcision, but this kicks off the loveliest recits, the bass meditating on that “sweet word” with soprano-led chorales punctuating and haloing his thoughts. The real star of the evening was young Ashley Riches, only two years out of the Royal Opera’s Jette Parker Young Artists programme, and the total artist: range secure from top to bottom, a highly dramatic way with the text and pure musicianship.

Tenor James Gilchrist has those last two qualities in abundance, but the lyric-tenor flow doesn’t come so easily to him these days. The aria “Ich will nur dir zu Ehren Leben” ("I will love only for Your honour") was a miracle of elegant runs, the rest patchier. As was the case with soprano Lorna Anderson, a late replacement for indisposed Susan Gritton, and mezzo Barbara Kozelj; uneven vocal production left us with some quiet stretches. But Anderson hit an expressive purple patch in tandem with oboist Frank de Bruine in the “Echo” aria adapted, like so much else in the sequence, from one of three earlier cantatas in praise of local potentates.

Too much is often made of the “parody” techniques whereby Bach reworked previous music into a different context. More importantly, the oratorio sequence is one of careful contrasts and a cornucopia of fascinating, highly varied instrumentation, from the drums and trumpets – the risk of capricious valveless instruments just about worth taking for the sheer beauty of tone – of the opening chorus through to the oboes da caccia (Mark Radcliffe and Oonagh Lee, pictured right) making up a pastoral group of four for the shepherds’ pastorals and a vigorous trio of solo strings. Cello and bass lines frequently rocked the Barbican, not the ideal setting for this work but more amenable to these small forces than to large symphony orchestras.

From the start, Egarr produced a crisp and even sound from his orchestra and chorus, always word-sensitive even if brighter sopranos would have reinforced the sheer jubilation of the first, third and sixth cantatas. So yes, well worth the shortcomings to celebrate the unflagging genius and spirit of the season’s greatest musical offering.

• The Academy of Ancient Music perform more cantatas by Bach in March 2016