To the end, in the hymns of the eighth, a psalm to David.
1. “Of the eighth,” seems here obscure. For the rest of this title is more clear. Now it has seemed to some to intimate the day of judgment, that is, the time of the coming of our Lord, when He will come to judge the quick and dead. Which coming, it is believed, is to be, after reckoning the years from Adam, seven thousand years: so as that seven thousand years should pass as seven days, and afterwards that time arrive as it were the eighth day. But since it has been said by the Lord, “It is not yours to know the times, which the Father has put in His own power:” and, “But of the day and that hour knows no man, no, neither angel, nor Power, neither the Son, but the Father alone:” and again, that which is written, “that the day of the Lord comes as a thief,” shows clearly enough that no man should arrogate to himself the knowledge of that time, by any computation of years. For if that day is to come after seven thousand years, every man could learn its advent by reckoning the years. What comes then of the Son's even not knowing this? Which of course is said with this meaning, that men do not learn this by the Son, not that He by Himself does not know it: according to that form of speech, “the Lord your God tries you that He may know;” that is, that He may make you know: and, “arise, O Lord;” that is, make us arise. When therefore the Son is thus said not to know this day; not because He knows it not, but because He causes those to know it not, for whom it is not expedient to know it, that is, He does not show it to them; what does that strange presumption mean, which, by a reckoning up of years, expects the day of the Lord as most certain after seven thousand years?
Source: The Enarrations, or Expositions, on the Psalms (New Advent)