Dearest brothers and sisters, we keep vigil on this night, on which we recall that our Lord was buried. We ought to keep vigil during that time in which, for our sakes, he slept. Long before, he announced his passion through his prophet: “I slept,” he says, “and I rose up, because the Lord received me” (Psalm 3:5). He called the Father “Lord.” Hence on the night on which he slept, we keep vigil, so that through the death he suffered we might have life. During his short sleep we celebrate a vigil, so that he will keep watch for us and, when we are raised, we can abide untired for the eternal vigil. On the night he also rose; our hope keeps watch for his resurrection.
St. Augustine, Sermon 223B
Locus Communis 