At school, the only subject I was any good at was music, and for the usual reason: an inspiring teacher. Phyllis Robinson, neé Chatfield, had been a famous concert pianist – and so I begged piano lessons. I practised assiduously, and finally got promotion to school pianist, with free tuition from the star herself. I particularly loved being accompanist to the many choirs she organised (I missed swathes of lessons as a result, of course, and "forgot to do" a lot of homework). We entered local choral contests and won prizes and commendations. But my happiest memory is of accompanying the junior choir's rehearsals for a Christmas performance of Benjamin Britten's Ceremony of Carols.

The piano-arrangement is tricky: I certainly couldn't play it now. But I can still sing the songs, suitably transposed. It was not only the spiky, sparkly freshness of the melodies and the clear, high voices of the junior choristers I found exciting. It was that English itself seemed reborn as a new language.

I'd experienced this before, but only in negative ways. We'd plodded grimly through Scott's Ivanhoe in the first form. We'd read the Iliad, in translation, and A Midsummer Night's Dream. I'm afraid I didn't feel any sense of revelation from either. It's a shameful admission. But then, nothing was explained properly (well, perhaps I wasn't listening) and we certainly didn't see any live performances. We took it in turns to read aloud, droning or stumbling and barely understanding a word of what we were reading. The verbal magic was assassinated. I hated "English".

I don't believe anyone told us that the carols in Britten's Ceremony were in Middle English. The odd diction didn't seem bookish: it was rough, at times, and full of vernacular energy. Britten, a great melodist, also finds fantastic rhythms in the songs, spicing them with a hot, unpredictable, Rite-of-Spring sensuality. Of course there were words I didn't understand, but since the emotional meaning was present, it wasn't an issue.

At 15, I'd already discovered Christmas was a big fat bourgeois cliché. Now, through those carols, I entered a cliché-free zone. A cynical teen atheist had reconnected to a long-discarded childish wonder – with added grown-up hormones.

I loved and still love those carols: "Adam lay ibounden", "Wolcum Yole", "There is No Rose". My favourite to read, though, is "I Sing of a Maiden." It's more beautiful on the page than in its musical setting. The white space around it heightens the focus on the perfectly pitched individual words. The last verse keeps the meditative atmosphere it tends to lose when sung. A hush like the hush of new snow hangs over the whole carol.

Although, on a good day, I'm an agnostic with atheist tendencies rather than the raging Ms Dawkins I was at 15, I read the poem now as I did then: as erotic myth. It centres on the immaculate conception, translating this event to an idealised local context. Mary enjoys an agency and freedom absent from the original story. The clue is in the little word "ches": she has chosen God for her son. Decoded, this suggests a voluntary relationship between woman and lover. Her defloration, tender, refined and entirely without violence, is a small miracle.

The carol says nothing about the physical realities of sex or childbirth. It talks instead of dew, spray, grass, flowers. Perhaps it hints at a contradictory wish for disembodied perfection at the heart of human desire. This dream comes alive in a Mary from courtly romance, in her delicately pastoral conception and blood-free confinement. In remembering the April origins of the December birth, the poet also draws our attention to the entrancing pleasures of the coming spring.

I Sing of a Maiden

I sing of a maiden
  That is makeless.
King of all kings
  To her son she ches.

He cam also stille
  Ther his moder was
As dewe in Aprille
  That falleth on the grass.

He cam also stille
  To his modres bowr
As dewe in Aprille
  That falleth on the flowr.

He cam also stille
  Ther his moder lay
As dewe in Aprille
  That falleth on the spray.

Moder and maiden
  Was never noon but she:
Well may swich a lady
  Godes mother be.

("Makeless"= matchless, mateless, spotless; "ches" = chose; "ther" = where)