Of course, Bach's worship music is a wee bit different from contemporary worship music. But one piece of Bach's music that's still rather well-known around the world today in a worship context is his harmonisation of the Passion Chorale (usually sung as O Sacred Head Once Wounded, Redemption Hymnal No. 162; Songs of Fellowship 446). (In fact, the melody of the Passion Chorale wasn't even written by Bach; he adapted an earlier melody and harmonised it to use in several of his works.) The Passion Chorale gets its names because it's used five times in the Saint Matthew Passion.
So, what is the St. Matthew Passion? At first glimpse it might seem like a rather long piece of music (it does last over three hours) but that misses what it really is, and what it's for. In fact, the Passion is a nearly complete church service. It's divided into two parts, between which was to be found the sermon. The point of the Passion was to have a Good Friday service focused on the Gospel account of the Cross. In fact that's what the words of the passion are: the Biblical text of Matthew chapters 26 and 27 interspersed with arias and chorales containing theological reflection or personal response to the Biblical text.
So, for example, after Pilate asks 'Why, what evil hath this man done?' and immediately before the crowd dramatically (in two choruses) replies 'Crucify Him!', a glorious aria explains:
For love now,
For love now would my Saviour perish,
Of any sin he knoweth nought.
That eternal condemnation
And the sentence of the court
Not upon my soul continue.
So, although the music might be a bit different from much modern worship music, and although the Passion form might be a bit unfamiliar to us today, at its heart it does the same thing that should be happening in our contemporary worship services: God's Word is proclaimed and God's people respond. In fact, perhaps it does even more than what we normally do; for in the Passion, the Word isn't only kept to the sermon portion between the two parts, but the Word is proclaimed throughout. There is a continual Gospel proclamation and response, as the Word of God itself dictates the form and stands as the foundation of the whole work. In all honesty, when was the last time we gave over so much time in a service to the reading of Scripture?
Anyway, Bach's St. Matthew Passion might not be the sort of worship music to which one can clap or dance along, but it is the sort of music to which one can worship in quiet contemplation as one listens. Listen to it in English (the Bach Choir conducted by Sir David Willcocks for an English version, or at least follow the English text while listening to a German version), and worship the Lamb of God who once was slain.