Composed for the First Sunday after Trinity, which fell on June 11, 1724, Bach's Cantata No. 20 "O Ewigkeit, du Donnerwort" (Oh, Eternity, you thunderous word) (BWV 20) is based on a hymn by Johann Rist (1642) interspersed by poetic paraphrases by an unknown author. Divided into two parts with a total of 11 movements, "O Ewigkeit, du Donnerwort" is one of Bach's larger cantatas. However, the higher number of movements is balanced by generally shorter movements; that is, arias without da capo and fewer extended recitatives. The cantata is scored for tenor, bass and alto soloists, chorus, a solo trumpet, three oboes, strings, and basso continuo. The cantata is in F major, with its first and seventh movements in the tonic, its second in C major, its third movement in C minor, its fourth and sixth movements in D minor, and its fifth in B flat major. The second part and eighth movement open in the dominant of C major, its ninth and tenth movements in A minor, and its second part and 11th movement end back in the tonic of F major. The first movement is in the form of a French overture, with stately double-dotted rhythms in common time followed by a fugal Vivace in triple time, with a recapitulation of the double-dotted opening at the close. In both sections of the first movement, the soprano intones the hymn tune while the lower choral voices add imitative embellishments. The second movement is a brief tenor recitative, followed by a sorrowful tenor aria with strings for the third movement. The fourth movement is a slightly longer bass recitative, followed by a more sanguine bass aria accompanied by the three oboes for the fifth movement. The sixth movement is a mournful aria for alto and strings. The first part of the cantata closes with a restrained setting of Rist's hymn. The second part of the cantata opens with a brilliantly scored bass aria for solo trumpet, with the oboes doubling the strings. Like the recitatives and arias of the first part, the brief ninth and tenth movements form a pair, the ninth being a brief alto recitative and the tenth a duet for alto and tenor over basso continuo. "O Ewigkeit, du Donnerwort" concludes with a straightforward harmonization of the hymn's closing lines for the entire chorus and orchestra. ~ James Leonard, All Music Guide
