"until I found the Well-Tempered Clavier"
 'The Well Tempered Clavier' is a collection of studies composed by Johann Sebastian Bach.  It is considered to consist of two books, each with 24 Preludes and Fugues.  The first collection was written in 1722, and the second, in 1742.  Bach created the pieces with the intention that they prove useful to students, and for experienced players as exercises to maintain form.  They were certainly a success in both these respects, but also had an immeasurable influence on Western Classical music.  Beethoven, Mozart and Verdi are all known to been guided by the pieces; Bach's innovations with the Fugues were especially significant.  It also influenced ideas about timing and the use of musical keys.

Bach's value as a teacher is shown in these lovely descriptions from pupils.

Listen to a piece from 'The Well Tempered Clavier'.