Given the following context:  Johann Sebastian Bach composed the church cantata Erschallet, ihr Lieder, erklinget, ihr Saiten! (Ring out, you songs; sound, you strings!), BWV 172, in Weimar for Pentecost Sunday in 1714. Bach led the first performance on 20 May 1714 in the Schlosskirche, the court chapel in the ducal Schloss. Erschallet, ihr Lieder is an early work in a genre to which he later contributed complete cantata cycles for all occasions of the liturgical year. Bach was appointed Konzertmeister in Weimar in the spring of 1714, a position that called for the performance of a church cantata each month. He composed Erschallet, ihr Lieder as the third cantata in the series, to a text probably written by court poet Salomon Franck. The text reflects different aspects of the Holy Spirit. The librettist included a quotation from the day's prescribed Gospel reading in the only recitative, and for the closing chorale he used a stanza from Philipp Nicolai's hymn "Wie schön leuchtet der Morgenstern" (1599). The work is in six movements, and scored for four vocal soloists, four-part choir, three trumpets, timpani, oboe, bassoon and a string orchestra of two violins, two violas, and basso continuo. The orchestra for the holiday occasion is festive compared to the two works previously composed in Weimar. The cantata opens with a chorus, followed by the recitative, in which words spoken by Jesus are sung by the bass as the vox Christi (voice of Christ). A bass aria with trumpets addresses the Trinity, and a tenor aria then describes the Spirit that was present at the Creation. This is followed by an intimate duet of the Soul (soprano) and the Spirit (alto), to which an oboe plays the ornamented melody of Martin Luther's hymn "Komm, Heiliger Geist, Herre Gott" and a solo cello provides the bass line. The theme of intimacy between God and Man is developed further in the following chorale, after which Bach specified an unusual repeat of the opening chorus. While Bach served as Thomaskantor – director of church music – in Leipzig from 1723, he...  answer the following question:  What is the last name of the person who served as Thomaskantor?
Bach