Bach, the organ virtuoso

A posthumous report on Bach's 1739 dedication of the Trost organ at the Altenburg palace church reads:

For an organist, to yield to the singing congregation is better than to have it his way. Only a few are able to direct the congregation as the old Bach could do, who, on the great organ in Altenburg, played the Credo hymn "Wir glauben all an einen Gott" in D minor, but for the second stanza lifted the congregation to E-flat minor, and for the third one even up to E minor. That, however, only a Bach and an organ in Altenburg could make happen. This, all of us are not, and have not.  

apud Christoph Wolff, Johann Sebastian Bach: The Learned Musician, p.144 ff