Continuous joy can only be experienced through continuous prayer and continuous thankfulness.
This is possible for the Christian since only he has reason to be joyful for, pray for, and be thankful for because when the judgment of God is poured upon the world, instead of suffering wrath, he will receive complete salvation, and even death will have no power to deny him resurrection and an imperishable body.
Such hope, which the best in the world cannot offer, can bring only pure joy.