Rejoice!

Happiness is the feeling of pleasure driven by circumstances. (e.g. I am happy because I have a job promotion.)

Joy is the feeling of pleasure beyond/in spite of circumstances - it is a conscious decision to be cheerful no matter what. (e.g. I am joyful even though I am very stressed at work.)

Are you happy or are you joyful?

Yesterday's sermon was one of the best sermons I have ever listened to. Will post the link here when it is available.