who had been prepared
οἱ ἡτοιμασμένοι [hoi hētoimasmenoi] , perfect tense passive participle, the ones having been prepared. The preparation was not their own, but that of God. God had actively held them in reserve for this specific time. They are reserved for use in judgment (Isa. Isa. 24:21-22; 2Pe. 2Pe. 2:4; Jude Jude 1:6). Indeed, God works all things according to the counsel of His will (Eph. Eph. 1:11).
for the hour and day and month and year
The one article and one preposition before the four times, unites them: . . . it denotes the appointed hour of the appointed day of the appointed month of the appointed year.1 They were to be released at the hour of His judgment (Rev. Rev. 14:7+), a time known only to God (Mark Mark 13:32; Acts Acts 1:7).2 This very moment, as we contemplate the text, these powerful angels and their related demonic horde are pent up awaiting their eventual release whereupon they will rush out upon an unsuspecting world to unleash hell on earth. The intensity of their malevolent thoughts and intentions likely escalates as they endure the ongoing frustration of their present captivity. What a horrific and fearsome judgment that will pour forth upon the earth dwellers at the time of the end!
to kill a third of mankind
A third of the population of the earth would be killed by these four angels and the army which they lead (Rev. Rev. 9:16-18+). Death will come by three means: fire, smoke, and brimstone. See commentary on Revelation 9:18.
The trumpet judgments share a pattern of affecting one-third of what they target. In the first trumpet judgment, a third of the trees were burned up (Rev. Rev. 8:7+). In the second trumpet judgment, a third of the sea became blood, a third of the creatures in the sea perish, and a third of the ships were destroyed (Rev. Rev. 8:8-9+). In the third trumpet judgment, a third of the rivers and springs are poisoned (Rev. Rev. 8:10-11+). In the fourth trumpet judgment, a third of the sun, moon, and stars were struck so as to be darkened (Rev. Rev. 8:12+). In the fifth and sixth trumpet judgments, all men without the seal of God are tormented, and then a third of them are killed.
When the second seal is opened, peace is taken from the earth and people kill one another (Rev. Rev. 6:4+). When the third seal is opened, there is great famine and presumably additional deaths occur (Rev. Rev. 6:5-6+). When the fourth seal is opened, Death and Hades kill a fourth of the earth (Rev. Rev. 6:8+). If the fourth of the earth describes a region, then we cant be sure what proportion of the total population dieit would depend upon the region and the distribution of the population. If we assume that roughly one fourth of the population remaining alive at the time of the third horsemans ride perish in the judgments of the third seal, then less that 75 percent of the original population prior to opening the first seal remains alive. (Some died during the judgments of the second and third seals.) Additional people die in the preceding trumpet judgments (ships are destroyed, men die from drinking poisoned waters, Rev. Rev. 8:9+, Rev. 8:11+). Here an additional third of the remaining population perish, or one-third of the less than 75 percent which remains. After the first six seal and six trumpet judgments, the population of the earth has been reduced by more than half.
If the first seal were loosed today [December 2003], using the current world population of over 6 billion, and neglecting those who will be removed from the earth in the Rapture prior to this time,3 more than 3 billion would have died by the end of the sixth trumpet in the judgments from God.4 No wonder Jesus said, For then there shall be great tribulation, such as has not been since the beginning of the world until this time, no, nor ever shall be. And unless those days were shortened, no flesh would be saved; but for the elects sake those days will be shortened (Mtt. Mat. 24:21-22).
2 Morris takes the time designation collectively as denoting a duration of their ministry lasting 13 months.