The chant and transcendental sequence Sobre un éxtasis de alta contemplación (Verses written after an ecstasy of high exultation), a setting of the poem by St John of the Cross, was commissioned by Richard Marlow for the Cambridge University Chamber Choir who gave its first performance at Selwyn College in November 1975. The piece marked a new direction in Harvey's music towards clarity of vision and simplicity of means, but the simplicity of Sobre and the complexity of earlier, germane works, such as Ludus amoris, are different manifestations of the same spiritual conviction.

The intense individuality of Harvey's music is characterised by emotional opulence and visionary symbolism, showing the profound impact made on him by the music of Messiaen and Stockhausen; indeed, his musical designs are frequently governed by serial operations similar to theirs.

The idea that humanity is enriched by experience of the divine is central to his artistic credo. It is therefore appropriate that in a number of vocal works Harvey should seek the writings of St John of the Cross (that most eloquent of mystic poets) for inspiration: Ludus amoris, On Vision and Sobre un éxtasis.

Harvey has attempted to recreate in musical terms the state of mysterious illusion enacted in the verses. The following extracts (translated by Roy Campbell) adequately convey the sense of the poem:

"I entered in, I know not where,
And I remained, though knowing naught,
Transcending knowledge with my thought…
So borne aloft, so drunken-reeling,
So rapt was I, so swept away,
Within the scope of sense or feeling
My sense in feeling could not stay.
And in my soul I felt, revealing
A sense that, though its sense was naught,
Transcended knowledge with my thought."

The music begins in traditional serial fashion. A rhythmic figure in the bass line, derived from the rhythm of the Spanish words, is partially augmented in each of the parts in ascending order so that the soprano line is twice the length of the beginning. This sets the pattern for the rhythmic counterpoint of the "chant" section. Contrast is provided by unison rhythmic textures which describe the divinity: "De paz y piedad era la sciencia perfecta" Of peace and piety interwound/This perfect science had been wrought).

Harmonically the music is dominated by the F major chord which can be understood as symbolising the human. Harvey has spoken of being fascinated by perfectly tuned voices, how they convey a sense which is "out of this world". Against the chord in verse two, the tenor soloist outlines the shape of a contrasting chord which, with its similarity to Wagner's Tristan chord or Scriabin's "Mystic" chord can be understood to represent the divine. The divine chord emerges in the choir at the close of the 'chant' section.

In the transcendental sequence beginning "Y es de tan alta excelencia aqueste sumo saber" (This summit all so steeply towers/And is of excellence so high) the rhythmic and harmonic symbols evolve from separateness to fusion in a climax so overpowering that nothing can follow but incoherent, fragmentary shouts and whispers.