When Bach obtained the post of kantor at the Thomaskirche, he embarked on one of his most ambitious projects: composing an original work for the entire liturgical year. Between 1723 and 1726, he produced a cantata for each Sunday. These cantatas were veritable laboratories for musical creation, with the composer lending them various vocal and instrumental ensembles. Within this repertoire, the alto voice takes on a special connotation, sometimes dolorous, sometimes fervent, and Bach gives it some of his most beautiful arias. Christophe Rousset and the countertenor Zoltan Darago explore this repertoire in a program drawn mainly from the abundant early years in Leipzig, which gives a great place to the concertante parts, featuring sublime dialogues between violin, oboe d'amore or organ and voice.