What will we do in heaven? I answer that our whole activity will consist in sing “amen” and “alleluia.” Refuse to be saddened by the thought that you if you remained standing and saying every day “amen” and “alleluia” you would collapse with weariness [boredom]. In heaven you will cry out “amen” and “alleluia” not simply with sounds from your throat but with the devotion of the heart. What then does amen mean? What does alleluia mean? Amen means “it is true!” Alleluia means “praise God!” Those things that Paul said we now see “through a mirror as a riddle” (1 Corinthians 13:12) we shall then see with an inexpressibly different feeling of love. We then will shout “Why, it’s true!” And because we shall see the truth with perpetual delight, we will be moved to praise God by shouting “alleluia!”

—Augustine, Sermon 362.1