His music is full of originality, wit, depth of feeling and craftsmanship. He was also influential as a keyboard teacher and his Essay on the True Art of Playing Keyboard Instruments was used by Beethoven for his students and is still in print today. Bach lived in a time of great change in musical style, from the learned fugue and counterpoint that his father J.S. Bach was master of, to a style more accessible, simple and tuneful, the Style Galante. Bach wrote over 800 pieces in many different forms, including the symphony.
Bach's symphonies are written in the Italianate style, that is they are in three movements and alternate fast-slow-fast, and are descended from overtures to operas. His other stylistic factor is that he does not follow style galante nearly as much as he follows empfindsamer Stil, or the sensitive style of composition. Bach's symphonies are the forerunners of the Romantic style in that they have more of a depth of feeling to them and are full of sudden changes of mood between the movements.
There's some question as to how many symphonies Bach wrote, but we do know that the Symphony in B Minor For Strings was fifth in a set of six string symphonies he wrote for Baron Gottfried van Swieten. Upon talking to Bach about the commission for the symphonies, the Baron told Bach to not be concerned about writing difficult music to perform. Evidently the Baron had a good orchestra at his disposal. The Baron was also a patron of three other great composers, Haydn, Mozart, and the young Beethoven.
The symphony is typical of Bach, with a first movement that flirts with the major and minor scales, is full of runs for the violins and outbursts for the entire ensemble. The second movement is a gently rocking larghetto that leads into the third movement presto with the orchestra scampering out a theme amid the outbursts from the high strings.