BWV 225 ("Sing unto the Lord a new song") is widely considered the greatest of the five motets firmly ascribed to Bach. With the single exception of BWV 228 ("Fürchte dich nicht, ich bin bei dir"), the purpose for which the motets were written is not known. However, the survival of Bach's autograph score and parts have in this instance allowed a dating of 1726 or 1727. Bach was under no obligation to provide motets for the Lutheran liturgy in Leipzig (which explains their small number in comparison with his huge output of cantatas), but it seems possible that all but the present work were written for funerals. An alternative and persuasive argument has been advanced by the great Bach scholar Christoph Wolff, who believes that motets such as the present work were written for didactic purposes -- to teach Bach's many pupils varying aspects of compositional and performance technique. Such a theory fits this complex and extraordinarily inventive motet very well, for it is a technical tour de force that makes considerable demands on its performers. The text consists of a typical juxtaposition of biblical (Psalms 149 and 150) and chorale texts (Johann Gramann's hymn "Wie sich ein Vat'r erbarmet" (1530), and an anonymous early eighteenth-century hymn), here augmented by an anonymous poetic text. The motet is cast in three distinct sections, fast, slow, and fast. It opens with an eight-part chorus, which after a homophonic introduction proceeds to a section in which one four-part choir is used to accompany a fugal development by the other, an extraordinary and at the time unique device. The central slower section is also layered and divided into two four-part choruses, with the anonymous poetic text freely juxtaposed with the stricter lines of the chorale melody. The final section initially returns to the animated homophony of the opening, but subsequently evolves into a four-part fugue with the two choirs combined. Unlike the cantatas, which quickly dropped from the repertoire after Bach's death, performances of the motets continued in Leipzig. In 1789, a performance of BWV 225 was mounted for Mozart when he visited the city; after hearing the motet, he is said to have exclaimed, "That is really something from which one can learn a great deal!" ~ Brian Robins, All Music Guide
