The winged messenger of day
Sings loud, foretelling dawn’s approach,
And Christ in stirring accents calls
Our slumbering souls to life in Him.
“Away,” He cries, “with dull repose,
The sleep of death and sinful sloth;
With hearts now sober, just, and pure
Keep watch, for I am very near.”
Prudentius, Hymns 1.1-8
He writes this as though to people already instructed. He compared the suddenness of the Lord’s coming to a thief, who tries to escape notice, but the one guarding the house detects the coming of the thief, whereas the one who is heedless and goes to sleep is robbed. In similar fashion the one keeping watch for the Lord’s return recognizes the signs.… The pregnant woman knows she is carrying an unborn child, but does not know the time of labor. So too in our case, the fact that the Lord of all will come we know, but we have not at all been given clear teaching about the time itself; hence we must always be on the lookout for that day.
Theodoret of Cyrus, Commentary on First Thessalonians