"For me, Bach is the greatest of preachers. His cantatas and Passions tune the soul to a state in which we can grasp the truth and oneness of things, and rise above everything that is paltry, everything that divides us." -- Charles-Marie Widor, from the Preface to the biography J. S. Bach by Albert Schweitzer

We all know that Bach is a technical wizard.  Counterpoint might be what he's best known for.  But if you want to convince someone of Bach's power as a spiritual storyteller, go to the chorales in the cantatas and Passions.   There you will find pieces like this, "O große Lieb" (O great love), where in four lines of text, Bach's harmonies perfectly paint the mood of each line of text, sometimes laser-targeted down to the very note.  

"O große Lieb" from St John Passion, Netherlands Bach Society, Jos van Veldhoven, conductor