Throughout his life, Bach showed exceptional talent as a pedagogue. As an orphan who had been obliged to learn everything by himself, he retained the deep-rooted urge to teach and pass on his knowledge. His cantatas are spiritual lessons, just as his keyboard works constitute a tutor in the instrument. It was with his children, first and foremost, that he exercised this talent as a born teacher, and particularly with his prodigiously gifted eldest son, Wilhelm Friedemann. For him he wrote the Two-part Inventions and Three-part Sinfonias; for him too The Well-Tempered Clavier and the Orgel-Buchlein (Little organ book); and this extraordinary method culminated in the Trio Sonatas for organ. The cantata Geist und Seele wird verwirret (Spirit and soul are dumbfounded) BWV 35 is one of the three written for solo alto without choral participation and with reduced instrumental forces. The work comprises two parts, for performance before and after the sermon. Soloist and organ engage in a dialogue charged with the elation of trust in God, brimming with coloratura passages and runs. Also for alto solo, the cantata Vergnugte Ruh, beliebte Seelenlust (Contented repose, beloved heart's desire) BWV 170 dates from just six weeks before Geist und Seele. It too features a solo organ part, later transcribed by Bach for flute and continuo. The cantata is based on a passage from the Sermon on the Mount in which Christ urges his listeners to live in peace with others.