1 Thessalonians 5:2

So what is this day which the Lord has made? Live good lives, and you will be this day yourselves. The apostle, you see, was not talking about the day which begins with sunrise and ends with sunset, when he said, "Let us walk honorably, as in the day"; where he also said, "For those who get drunk are drunk at night." Nobody sees people getting drunk at the midday meal; but when this does happen, it is a matter of the night, not of the day which the Lord has made. You see, just as that day is realized in those who live godly, holy and righteous lives, marked by moderation, justice, sobriety. So too on the contrary, for those who live in an ungodly, loose-living, proud and irreligious manner—for that sort of night, the night will undoubtedly be a thief. "The day of the Lord will come just like a thief in the night."

"But concerning the times and the seasons, brethren, ye have no need that aught be written unto you. For yourselves know perfectly that the day of the Lord so cometh as a thief in the night." Nothing, as it seems, is so curious, and so fondly prone to pry into things obscure and concealed, as the nature of men. And this is wont to happen to it, when the mind is unsettled and in an imperfect state. Why has he not said that no one knows? why has he not said, that it is not revealed, instead of saying, "Ye have no need that aught be written unto you"? Because in that case he would have grieved them more, but by speaking thus he comforted them. For by the expression, "Ye have no need," as if it were both superfluous, and inexpedient, he suffers them not to enquire. For tell me, what would be the advantage? Let us suppose that the end would be after twenty or thirty or a hundred years, what is this to us? Is not the end of his own life the consummation to every individual? Why art thou curious, and travailest about the general end? But the case is the same with us in this, as in other things. For this reason Christ did not tell it, because it was not expedient. Hear Paul saying, "For yourselves know perfectly that the day of the Lord so cometh as a thief in the night." Not the general day only, but that of every individual. For the one resembles the other, is also akin to it. For what the one does collectively, that the other does partially. For the period of consummation took its beginning from Adam, and then is the end of the consummation; since even now one would not err in calling it a consummation.

Do not place your confidence in your youth, nor think that you have a very fixed term of life, "For the day of the Lord comes as a thief in the night." On this account he has made our end invisible, so that we might demonstrate clearly our diligence and forethought. Do you not see men taken away prematurely day after day? On this account a certain one admonishes, "don't delay in turning to the Lord, and don't put things off from day to day," lest at any time, while you delay, you are destroyed. Let the old man keep this admonition; let the young man heed this advice. Indeed, are you in insecurity, and are you rich, and do you abound in wealth, and does no affliction happen to you? Still hear what Paul says: "when they say peace and safety, then sudden destruction comes upon them." Affairs change often. We are not masters of our end. Let us be masters of virtue. Our Master Christ is loving.

The apostle says: "The day of the Lord shall so come as a thief in the night. When they shall say, Peace and security, then on them shall come sudden destruction." [1 Thessalonians 5:2-3] Also in the Acts of the Apostles: "No one can know the times or the seasons which the Father has placed in His own power." [Acts 1:7]

By the Day of the Lord one must understand both the general end and the particular end of each person, for this latter is also unknown as to when it will come for each one. And this is beneficial for us for many reasons. First, …