What does the teacher mean by "joking" at the end of the movie Confessions?

On the one hand, it echoes the madness of the young Xiuzai, and on the other hand, it stimulates Xiuzai's nerves. It means that I was joking when I said you would be born again. I wish you always live in sin and pain, suffer and never live out of life. At the end of this cruel sentence, people can't help shivering, thus pushing the revenge effect of Moriguchi teacher to the extreme!