For Jesus, the demand for joy is a way to live with suffering and to outlast suffering. Therefore, this joy is serious. It's the kind you fight for by cutting off your hand (Matthew 5:30) and selling your possessions (Matthew 13:44) and carrying a cross with Jesus to Calvary (Matthew 10:38-39). It has scars. It sings happy songs with tears. It remembers the dark hours and knows that more are coming. The road to heaven is a hard road, but it is not joyless.
---John Piper, In Our Joy, pg 35