Because there are these two periods of time — the one that now is, beset with the trials and troubles of this life, and the other yet to come, a life of everlasting serenity and joy — we are given to liturgical seasons, one before Easter and the other after. The season before Easter signifies the troubles in which we live here and now, while the time after Easter which we are celebrating at present signifies the happiness which will be ours in the future. What we commemorate before Easter is what we experience in this life; what we celebrate after Easter points to something we do not yet possess. This is why we keep the first season with fasting and prayer; but now the fast is over and we devote the present season to praise. Such is the meaning of the Alleluia we sing.
Both these periods are represented and demonstrated to us in Christ our head. The Lord's passion depicts for us our present life of trial — shows how we must suffer and be afflicted and finally die. The Lord's resurrection and glorification show us the life that will be given to us in the future.
Now therefore, brethren, we urge you to praise God. That is what we are all telling each other when we say Alleluia. You say to your neighbor "Praise the Lord!" And he says the same to you. We are all urging one another to praise the Lord, and thereby doing what each of us urges the other to do. But see that your praises come from your whole being; in other words, that you praise God not with your lips and voices alone, but with your minds and lives and all your actions.
We are praising God now, assembled as we are here in this church; but when we go on our various ways again, it seems as if we cease to praise God. But provided we do not cease to live a good life, we shall always be praising God. You cease to praise God only when you swerve from justice and from what is pleasing to God. If you never turn away from the good life, your tongue maybe silent but your actions will cry aloud, and God will perceive your intentions; for as our ears hear each other's voices, so to gods years here are thoughts.
— Sermon of Saint Augustine on Psalm 148 for the feast of Easter.