(O holy bath of Spirit and water), 165, is a church cantata by Johann Sebastian Bach. He composed it in Weimar for Trinity Sunday and led the first performance on 16 June 1715. Bach had taken up regular cantata composition a year before when he was promoted to concertmaster at the Weimar court, writing one cantata per month to be performed in the , the court chapel in the ducal Schloss. was his first cantata for Trinity Sunday, the feast day marking the end of the first half of the liturgical year. The libretto by the court poet Salomo Franck is based on the day's prescribed gospel reading about the meeting of Jesus and Nicodemus. It is close in content to the gospel and connects the concept of the Trinity to baptism. The music is structured in six movements, alternating arias and recitatives, and scored for a small ensemble of four vocal parts, strings and continuo. The voices are combined only in the closing chorale, the fifth stanza of Ludwig Helmbold's hymn "", which mentions scripture, baptism and the Eucharist, in a summary of the cantata's topic. Based on the text full of Baroque imagery, Bach composed a sermon in music, especially in the two recitatives for the bass voice, and achieved contrasts in expression. He led the first performance, and probably another on the Trinity Sunday concluding his first year as Thomaskantor in Leipzig on 4 June 1724. Background On 2 March 1714 Bach was appointed (concert master) of the Weimar (court chapel) of the co-reigning dukes Wilhelm Ernst and Ernst August of Saxe-Weimar. The position was created for him, possibly on his demand, giving him "a newly defined rank order" according to Christoph Wolff. From 1695, an arrangement shared the responsibility for church music at the (court church) between the Samuel Drese and the Georg Christoph Strattner, who took care of one Sunday per month while the served on three Sundays. The pattern probably continued from 1704, when Strattner was succeeded by Drese's son Johann Wilhelm. When Bach also assumed the principal responsibility for one cantata a month, the 's workload was further reduced to two Sundays per month. The performance venue on the third tier of the court church, in German called (Heaven's Castle), has been described by Wolff as "congenial and intimate", calling for a small ensemble of singers and players. Performers of the cantatas were