The text is from this year's Gospel reading for Advent 1, Mark 13: 35-37. A beautiful rendition.
nescitis enim quando dominus domus veniat,
sero, an media nocte, an gallicantu, an mane.
ne cum venerit repente, inveniat vos dormientes.
Quod autem dico vobis,
omnibus dico: vigilate.
Watch ye therefore
(for you know not when the lord of the house cometh,
at even, or at midnight, or at the cock crowing, or in the morning):
lest coming on a sudden, he find you sleeping.
And what I say to you,
I say to all: Watch.