A kaleidoscope of styles – Bach’s Little Organ Book completed

The empty Orgelbuchlein page for Wir glauben all' an einen Gott, from the manuscript in the Berlin State Library (see below)   The late Professor Peter Williams, a renowned Bach scholar, once said 'How can we know what is in the head of an eighteenth-century Lutheran?'  He was replying to a question about Bach's intentions in a certain piece, and although Bach leaves few explicit insights into his creative processes, with his Orgelbüchlein (Little Organ Book) we do have more clues than usual.  Its purpose was firstly didactic.  'In which a beginning organist receives instruction as…