Johann Sebastian Bach directed his cantata O Ewigkeit, du Donnerwort, BWV 20 in Leipzig on the first Sunday after Trinity, beginning his chorale cantata cycle.

Johann Sebastian Bach was a German composer and musician of the late Baroque period. He is known for his prolific output across a variety of instruments and forms, including the orchestral Brandenburg Concertos; solo instrumental works such as the cello suites and sonatas and partitas for solo violin; keyboard works such as the Goldberg Variations and The Well-Tempered Clavier; organ works such as the Schübler Chorales and the Toccata and Fugue in D minor; and choral works such as the St Matthew Passion and the Mass in B minor. Since the 19th-century Bach Revival, he has been widely regarded as one of the greatest composers in the history of Western music.

Johann Sebastian Bach composed the church cantata O Ewigkeit, du Donnerwort, BWV 20, in Leipzig for the first Sunday after Trinity, which fell on 11 June in 1724. Bach composed it when beginning his second year as Thomaskantor in Leipzig. It is the first cantata he composed for his second annual cycle which was planned to contain chorale cantatas, each based on a Lutheran hymn. The cantata is focused on Johann Rist's 1642 hymn "O Ewigkeit, du Donnerwort", with a chorale melody by Johann Schop. The topic of death and eternity matches the Gospel for the Sunday, the parable of the Rich man and Lazarus.

Leipzig is the most populous city in the German state of Saxony. The city has a population of 628,718 inhabitants as of 2023. It is the eighth-largest city in Germany and is part of the Central German Metropolitan Region. The name of the city is usually interpreted as a Slavic term meaning place of linden trees, in line with many other Slavic placenames in the region.