Revelation 9:15 - Ellicott's Commentary On The Whole Bible

And the four angels... — Better, And there were loosed the four angels who had been made ready unto (or for, i.e., ready for) the (not “an hour,” but the) hour, and day, and month, and year, that they should slay the third part of mankind. The English version reads as though the hour, day, month and year were to be understood as the length of time over which this plague of war should last. This idea has been adopted by many of the historical school of interpreters, and great ingenuity has been exercised to find some period which exactly corresponds with this, and during which disastrous wars prevailed. But the expression (“made ready unto the hour,” &c.) is not to be taken to imply that such was the duration of the plague; it implies that the loosing of the angels would take place at a definite period, the year, month, day and hour of which were known; the expression corresponds somewhat with our Lord’s words, “Of that day and hour knoweth no man.” It reminds us that there is a period — an unknown period, but nevertheless a certain period — at which the latent powers of retribution wake and begin to avenge themselves, at which the restraints which have withheld the long-deserved scourges are removed. Men and nations little think of this. Peace they cry, where there is no peace, for they have been by their sins mining the ground under their feet, or dwelling in that abode of false security which Bunyan might have called the city of Meanwell, and that abode is built on the sands; and when the angels of judgment are loosed, and the restraining influences of public opinion broken, the tempest is abroad, the frail house of formal religion falls, and the time of testing leaves its inmates unsheltered. Happy only are they who are ready for the hour of the Lord’s return. The angels are made ready that they should kill the third part of mankind. The way in which this slaughter is to take place is explained in Revelation 9:17-18 : it is a wide and devastating slaughter carrying away a large portion of the human race.