Cantata BWV 2, entitled Ach Gott, vom Himmel sieh darein ("Oh God, look down from heaven"), is a choral cantata (Choralkantate) and the second work in the cycle of choral cantatas that Bach composed in 1724-1725 in Leipzig, where he had been Thomaskantor since 1723. It was composed in 1724 and premiered on 18 June 1724 in Leipzig. It was composed to be performed on the second Sunday after Trinity. The prescribed readings for that day included the First Epistle of John (1 John 3:13-18, on brotherly love) and the Gospel of Luke (Luke 14:16-24, the parable of the great banquet).
The cantata is based on Martin Luther's hymn Ach Gott, vom Himmel sieh darein, published in 1524 in the Achtliederbuch (the first Lutheran hymnal). This hymn is a paraphrase of Psalm 12 and consists of six stanzas. Bach used the text of the hymn literally in the outer movements (stanza 1 in the opening chorus and stanza 6 in the final chorale). An unknown librettist (a contemporary, probably the same one who wrote other cantatas in the cycle) paraphrased the ideas in the middle stanzas to create recitatives and arias that would fit the style of the cantatas in the first cycle, relating them to the readings of the day.
The cantata consists of six movements, typical of the choral cantata format of the 1724/25 cycle:
- Chorus – Ach Gott, vom Himmel sieh darein (stanza 1 of the hymn, in the style of an early motet with cantus firmus in the alto voice, strict four-part texture with independent continuo).
- Recitative (tenor).
- Aria (contralto/mezzo-soprano).
- Recitative (bass).
- Aria (tenor).
- Choral – Das wollst du, Gott, bewahren rein (verse 6 of the hymn, in four-part harmony).
The opening chorus stands out for its archaic treatment (Renaissance/neomotet style), with the cantus firmus in the alto voice and trombones doubling the choir voices.
In terms of instrumentation, the presence of four trombones doubling the choir voices in the opening and closing movements is noteworthy, lending a solemn and ancient colour that contributes to the serious and penitential character of the work, in keeping with the text of Psalm 12 and the supplicatory tone of the hymn.