Joy is not the same as happiness, not warm, not comfortable. It is unsettling, difficult, painful even.
Happiness belongs to the world; like the things of the world it can fade. Joy is of the spirit; it exists of itself, intense, in the spirit.
Bach knew about joy. His Heaven shines glorious in his music, searching, yet certain of the outcome, restless, yet at peace, yearning and fulfilment in one.