Herr Gott, nun schleuss den Himmel auf, BWV 1092

I can't describe this piece better than the website of All of Bach does:
‘Laß fahren, was auf Erden, will lieber selig werden.’ With a long, descending garland of notes at the end of this chorale, Bach illustrates the refrain of the text: the motto 'though life was hard, salvation awaits in heaven' (in major!). Simeon, who is speaking here, stands for all faithful Christians when he realises that the coming of Jesus means a crucial change of course. But before reaching that point, Bach combines all sorts of motifs he had picked up from around him as a young organist – with intriguing results. There are static chords broken by rests, a simple harmonisation of the first chorale phrase and then a repeat of this phrase, now accompanied by broken chords. The runs like intermezzi create a bewildering listening experience.

Played on the model of the Wender organ, Arnstadt. Since this piece was composed by Bach when he was young, this organ is very appropriate for this piece.