You see how many advantages there are, and yet there are more than these that arise from not knowing the time of our end. Meanwhile it is sufficient to learn these. On this account He so comes as a thief in the night; that we may not abandon ourselves to wickedness, nor to sloth; that He may not take from us our reward. “For yourselves know perfectly,” he says. Why then are you curious, if you are persuaded? But that the future is uncertain, learn from what Christ has said. For that on this account He said it, hear what he says, “Watch therefore: for you know not at what hour” the thief “comes.” On this account also Paul said,
Ver. 3. “When they are saying peace and safety, then sudden destruction comes upon them, as travail upon a woman with child; and they shall in nowise escape.”
Here he has glanced at something which he has also said in his second Epistle. For since they indeed were in affliction, but they that warred on them at ease and in luxury, and then while he comforted them in their present sufferings by this mention of the Resurrection, the others insulted them with arguments taken from their forefathers, and said, When will it happen?— which the Prophets also said, “Woe unto them that say, Let him make speed, let God hasten his work, that we may see it: and let the counsel of the Holy One of Israel come, that we may know it!”; and again “Woe unto them that desire the day of the Lord.” He means this day; for he does not speak simply of persons who desire it, but of those who desire it because they disbelieve it: and “the day of the Lord,” he says, “is darkness, and not light”— see then how Paul consoles them, as if he had said, Let them not account their being in a prosperous state, a proof that the Judgment is not coming. For so it is that it will come.
But it may be worth while to ask, If Antichrist comes, and Elias comes, how is it “when they say Peace and safety,” that then a sudden destruction comes upon them? For these things do not permit the day to come upon them unawares, being signs of its coming. But he does not mean this to be the time of Antichrist, and the whole day, because that will be a sign of the coming of Christ, but Himself will not have a sign, but will come suddenly and unexpectedly. For travail, indeed, you say, does not come upon the pregnant woman unexpectedly: for she knows that after nine months the birth will take place. And yet it is very uncertain. For some bring forth at the seventh month, and others at the ninth. And at any rate the day and the hour is uncertain. With respect to this therefore, Paul speaks thus. And the image is exact. For there are not many sure signs of travail; many indeed have brought forth in the high roads, or when out of their houses and abroad, not foreseeing it. And he has not only glanced here at the uncertainty, but also at the bitterness of the pain. For as she while sporting, laughing, not looking for anything at all, being suddenly seized with unspeakable pains, is pierced through with the pangs of labor— so will it be with those souls, when the Day comes upon them.
“And they shall in nowise escape.” As he was saying just now.
Ver. 4. “But you, brethren, are not in darkness, that that day should overtake you as a thief.”
Here he speaks of a life that is dark and impure. For it is just as corrupt and wicked men do all things as in the night, escaping the notice of all, and inclosing themselves in darkness. For tell me, does not the adulterer watch for the evening, and the thief for the night? Does not the violator of the tombs carry on all his trade in the night? What then? Does it not overtake them as a thief? Does it not come upon them also uncertainly, but do they know it beforehand? How then does he say, “You have no need that anything be written unto you”? He speaks here not with respect to the uncertainty, but with respect to the calamity, that is, it will not come as an evil to them. For it will come uncertainly indeed even to them, but it will involve them in no trouble. “That that Day,” he says, “may not overtake you as a thief.” For in the case of those who are watching and who are in the light, if there should be any entry of a robber, it can do them no harm: so also it is with those who live well. But those who are sleeping he will strip of everything, and go off; that is, those who are trusting in the things of this life.
Ver. 5. “For you are all,” he says, “sons of light, and sons of the day.”
And how is it possible to be “sons of the day”? Just as it is said, “sons of destruction” and “sons of hell.” Wherefore Christ also said to the Pharisees, “Woe unto you— for you compass sea and land to make one proselyte, and when he has become so, you make him a son of hell.” And again Paul said, “For which things' sake comes the wrath of God upon the sons of disobedience.” That is, those who do the works of hell and the works of disobedience. So also sons of God are those who do things pleasing to God; so also sons of day and sons of light, those who do the works of light. “And we are not of the night nor of darkness.”
Ver. 6, 7, 8. “So then let us not sleep, as do also the rest, but let us watch and be sober. For they that sleep sleep in the night; and they that be drunken are drunken in the night. But let us, since we are of the day, be sober.”
Here he shows, that to be in the day depends on ourselves. For here indeed, in the case of the present day and night, it does not depend on ourselves. But night comes even against our will, and sleep overtakes us when we do not wish it. But with respect to that night and that sleep, it is not so, but it is in our power always to have it day, it is in our power always to watch. For to shut the eyes of the soul, and to bring on the sleep of wickedness, is not of nature, but of our own choice. “But let us watch,” he says, “and be sober.” For it is possible to sleep while awake, by doing nothing good. Wherefore he has added, “and be sober.” For even by day, if any one watches, but is not sober, he will fall into numberless dangers, so that sobriety is the intensity of watchfulness. “They that sleep,” he says, “sleep in the night, and they that be drunken are drunken in the night.” The drunkenness he here speaks of is not that from wine only, but that also which comes of all vices. For riches and the desire of wealth is a drunkenness of the soul, and so carnal lust; and every sin you can name is a drunkenness of the soul. On what account then has he called vice sleep? Because in the first place the vicious man is inactive with respect to virtue: again, because he sees everything as a vision, he views nothing in its true light, but is full of dreams, and oftentimes of unreasonable actions: and if he sees anything good, he has no firmness, no fixedness. Such is the present life. It is full of dreams, and of phantasy. Riches are a dream, and glory, and everything of that sort. He who sleeps sees not things that are and have a real subsistence, but things that are not he fancies as things that are. Such is vice, and the life that is passed in vice. It sees not things that are, that is, spiritual, heavenly, abiding things, but things that are fleeting and fly away, and that soon recede from us.
But it is not sufficient to watch and be sober, we must also be armed. For if a man watch and is sober, but has not arms, the robbers soon dispatch him. When therefore we ought both to watch, and to be sober, and to be armed, and we are unarmed and naked and asleep, who will hinder him from thrusting home his sword? Wherefore showing this also, that we have need of arms, he has added:
Ver. 8. “Putting on the breastplate of faith and love: and for a helmet the hope of salvation.”
Source: Homilies on First Thessalonians (New Advent)