The purpose of the Gospel is not to make us happy (as the world defines it, e.g., positive emotions), but to make us holy. And this holiness is what divine Joy looks like.
The way I see it, misery is pain that is embittered with resentment and fueled by selfishness. Suffering is pain that is sweetened with forgiveness and empowered by love. In this world (and in the next) there will be pain and hardship. But the Love of God can transform that pain from misery to suffering, by making us whole in our hearts and holy in our souls.