Erforsche mich, Gott, und erfahre mein Herz , BWV 136

Erforsche mich, Gott, und erfahre mein Herz (Examine me, God, and know my heart), BWV 136 is a church cantata by Johann Sebastian Bach. Bach composed the cantata in 1723 in Leipzig to be used for the eighth Sunday after Trinity. He led the first performance on 18 July 1723.

The work is part of Bach's first annual cycle of cantatas. He began to compose cantatas for all occasions of the liturgical year when he took up office as Thomaskantor in May 1723. The cantata is structured in six movements: two choral movements at the beginning and end frame a sequence of alternating recitatives and arias. The opening movement is based on a verse from Psalm 139; the closing chorale on a stanza from Johann Heermann's hymn "Wo soll ich fliehen hin". The cantata is scored for three vocal soloists (alto, tenor and bass), a four-part choir, corno, two oboes, strings and basso continuo.

When Bach took up office as Thomaskantor (director of church music) in Leipzig in May 1723 on the first Sunday after Trinity, he began to compose cantatas for all occasions of the liturgical year. He wrote Erforsche mich, Gott, und erfahre mein Herz for the Eighth Sunday after Trinity. The prescribed readings for the Sunday are from the Epistle to the Romans, "For as many as are led by the Spirit of God, they are the sons of God" (Romans 8:12–17), and from the Gospel of Matthew, the warning of false prophets from the Sermon on the Mount (Matthew 7:15–23). An unknown librettist wrote the text, closely related to the prescribed gospel. His text is the first in a group of ten cantatas following the same structure of biblical text – recitative – aria – recitative – aria – chorale. The ten cantatas were dedicated to the 8th to 14th and 21st to 22nd Sunday after Trinity and the second Sunday after Easter.

The opening chorus is based on Psalms 139:23, focused on the examination of the believer's heart by God. The closing chorale is the ninth stanza of Johann Heermann's hymn "Wo soll ich fliehen hin" (1630) on the melody of "Auf meinen lieben Gott", which Bach used again in 1724 as the base for his chorale cantata Wo soll ich fliehen hin, BWV 5.

The Bach scholar Alfred Dürr concludes from the autograph that only the middle section of the third movements and the chorale were composed in 1723 with certainty. The other parts may rely on a former unknown secular or church cantata, according to the conductor John Eliot Gardiner and the musicologist Tadeshi Isoyama.

The cantata in six movements is scored for three vocal soloists (alto (A), tenor (T) and bass (B)), a four-part choir (SATB), corno (horn, Co), two oboes (Ob), two violins (Vl), viola (Va) and basso continuo (Bc). One oboe is marked "d'amore" (Oa) in the autograph kept by the Staatsbibliothek zu Berlin. Some scholars, including Dürr and Gardiner, believe that the second oboe part in the choral movements 1 and 6 should also be played by oboe d'amore. The title on the original parts reads: "Domin: 8 post Trinit: / Erforsche mich Gott, und erfahre mein ect. / â / 4 Voci / Corno / 2 Hautbois / 2 Violini / Viola / e / Continuo / di Sign: / J.S.Bach".

In the following table of the movements, the scoring and keys and time signatures are taken from Alfred Dürr, using the symbol for common time (4/4). The instruments are shown separately for winds and strings, while the continuo, playing throughout, is not shown.

The opening chorus expands on a psalm verse, "Erforsche mich, Gott, und erfahre mein Herz" (Examine me, God, and discover my heart). The music in the style of a Gigue expresses confidence facing the examination. In 1739 it was characterized by Johann Mattheson 1739 as "somewhat like the rapid arrow of a stream" ("etwa wie der glattfortschiessende Strom-Pfeil eines Bachs"). The movement is structure in two parts (A and A'), with choral fugues on the same themes, both presenting the complete text. An extended instrumental ritornello, dominated by the horn, is heard before, between and after the choral sections. The first fugue is preceded by a choral Devise (statement). Throughout the movement the two oboes never play independently but double the violins in the ritornelli and the soprano in the vocal sections. The virtuoso horn parts may have been intended for the exceptional Gottfried Reiche.

Bach used the same material as in this movement later in the "Cum Sancto Spiritu" of his Missa in A major.

A secco recitative, "Ach, daß der Fluch, so dort die Erde schlägt" (Alas, that the curse, which strikes the earth there), renders a contrasting change of mood. Bach interprets the curse of sin, and the hopeless situation of the humans and the threat of the Last Judgment in music full of dissonances.

The alto aria, "Es kömmt ein Tag" (A day will come), is accompanied by an oboe, an oboe d'amore according to Alfred Dürr and John Eliot Gardiner. The middle section, "Denn seines Eifers Grimm vernichtet" (For the wrath of His vengeance will annihilate), is certainly composed in 1723. The middle section is marked Adagio and in common time, contrasting to the first section, marked with Presto and with a 12/8 time signature.

A secco recitative, "Die Himmel selber sind nicht rein" (The heavens themselves are not pure), tends to an arioso in the last measures.

The violins in unison accompany the duet of tenor and bass, "Uns treffen zwar der Sünden Flecken" (Indeed, the stains of sin cling to us). The voices sing sometimes in imitation, sometimes in homophony, in the style of duets Bach wrote at Köthen earlier in his career.

The chorale, "Dein Blut, der edle Saft" (Your blood, the noble juice), is expanded to five parts with a combination of the four-part chorus and an accompanying violin part, similar to the chorale of Erschallet, ihr Lieder, erklinget, ihr Saiten! BWV 172, written earlier by Bach for Pentecost 1714 in Weimar.

The entries to the following listing are taken from the selection on the Bach Cantatas Website. Instrumental groups playing period instruments in historically informed performances are marked green.