Student or Learner
Does "that was the secret joke of this soul" refer to "that was the secret joke of Kant"?
The exact nature of Kant's religious ideas continue to be the subject of especially heated philosophical dispute, with viewpoints ranging from the idea that Kant was an early and radical exponent of atheism who finally exploded theontological argument for God's existence, to more critical treatments epitomized by Nietzsche who claimed that Kant had "theologian blood" and that Kant was merely a sophisticated apologist for traditional Christian religious belief, writing that "Kant wanted to prove, in a way that would dumbfound the common man, that the common man was right: that was the secret joke of this soul."
Yes. The phrase "that was the secret joke of this soul" refers to Kant. One clue to that, of course, is that the article is about Kant.