This work is based on the chorale tune "Ach Gott vom Himmel sieh darein" (Oh God of heaven look upon us). Of course, Bach did not merely do take-offs on the source themes in his chorale preludes and chorale fantasias, for he also attempted to capture the character suggested by the chorale's text. Here, the mood is rather somber throughout in its rather stately and grandiose treatment of the theme. But Bach imparts a celestial sense to the music as well, wringing from its chord-drenched textures, bass-laden sonorities, and often austere-sounding tones a reverence and religious sense whose fervor achieves an almost trance-like bliss. The work opens with the chorale theme mostly played in solemn chords that invoke a mood of contemplation, the music slowly moving along in an almost march-like manner. The mood brightens somewhat around midway through, as sonorities rise higher on the keyboard, but the sense of deep reverence and religious meditation remain. As the music proceeds, it develops a greater sense of ecstasy, Bach's contrapuntal writing deftly underscoring the rapturous atmosphere. This chorale prelude gloriously ends with a series of powerful, sustained chords that grandly ring out.

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