(Why do you trouble yourself, my heart), BWV 138', is a church cantata by Johann Sebastian Bach. He composed it for the 15th Sunday after Trinity and first performed it on 5 September 1723 in Leipzig. The text by an unknown author includes three stanzas from the hymn of the same name. Its text and melody were formerly attributed to Hans Sachs, but were written by an unknown hymn writer. The cantata has seven movements and is scored for SATB soloists and choir, two oboes d'amore, two violins, viola and basso continuo. The cantata has features of a chorale cantata although it was written a year before Bach's annual cycle of chorale cantatas. Bach used an aria as the base of the of his Missa in G major.