Jeremy Denk on Bach as reactionary:
Bach is distilled Something Else. He composed against the currents of his day; he swam upstream; he was a reactionary (for example: composing elaborate difficult counterpoint when the musical world was simplifying into homophony). His genius, according to the usual view, is not that of inventor or destroyer, but belongs to that colder virtue of perfection. Separation from Time is part of the Bach myth; against his island of perfection the vicissitudes of music history uselessly and cyclically break their waves. He ushers in no new Style, no Movement, no Ism; he opens the door to no Revolution; and therefore he is “pointless,” historically speaking. He would not “Stick it to the Man;” he is The Man.
On the contrast in Bach’s D major Partitas:
The minor keys in the major movements of the D major Partitas do not seem to oppose the prevailing mood but to fill it out; these momentary sadnesses seem to make the overall joy believable. …. The turn to major arises from the confirmation of minor; sadness is a cause for celebration and vice versa; the happier and sadder moments do not rebut each other, they are no dialectic; even the terms “happy” and “sad” may not be applicable; they each draw on the other, and blur the other, in a chain of logic, inspiration and cause.
I recommend grabbing the Partita No. 4 in D Major (BWV 828) by Gould immediately. Listen out for the humming.
Contrast makes overall joy more believable.