What are the three woes of Revelation?
The three woes of Revelation are announced in Revelation 8:13 and correspond to the last three trumpet judgments: the fifth trumpet is the first woe, the sixth trumpet is the second woe, and the seventh trumpet brings the third woe.
Before the final three trumpets sound, an angel flies through heaven crying, "Woe, woe, woe, to the inhabiters of the earth by reason of the other voices of the trumpet of the three angels, which are yet to sound!" This sets up the pattern that the fifth, sixth, and seventh trumpets are each marked as a woe upon the earth.
The first woe comes with the fifth trumpet, when a star falls from heaven and is given the key of the bottomless pit, releasing locust like creatures with the shape of horses prepared for battle, crowns like gold, faces of men, hair like women, teeth like lions, breastplates of iron, and stings like scorpions in their tails. Their king is Apollyon, the angel of the bottomless pit. They are given power to torment men for five months, not to kill them, so that men will seek death and not find it. At the close of this section it is written, "One woe is past; and, behold, there come two woes more hereafter."
The second woe comes with the sixth trumpet. Four angels bound at the great river Euphrates are loosed, prepared for an hour, a day, a month, and a year, to slay a third of mankind. They lead an army of two hundred thousand thousand horsemen, with breastplates of fire, jacinth, and brimstone, and fire, smoke, and brimstone issuing from the horses mouths, by which a third of men are killed. Even after this devastation, the rest of mankind does not repent of worshiping idols or of their murders, sorceries, fornication, and thefts. This second woe stretches on to include the ministry, death, and resurrection of the two witnesses in Jerusalem, and it closes with the words, "The second woe is past; and, behold, the third woe cometh quickly."
The third woe arrives with the seventh trumpet. Great voices in heaven declare, "The kingdoms of this world are become the kingdoms of our Lord, and of his Christ; and he shall reign for ever and ever." The nations are angry, the wrath of God comes, the dead are judged, reward is given to the prophets and saints, and those who destroy the earth are themselves destroyed. This is the point where the rule of the Antichrist and Satan begins to transition to the reign of Christ, and it is at this trumpet that the temple in heaven opens to reveal the ark of the testament, along with lightnings, voices, thunderings, an earthquake, and great hail.
The scriptures
And I beheld, and heard an angel flying through the midst of heaven, saying with a loud voice, Woe, woe, woe, to the inhabiters of the earth by reason of the other voices of the trumpet of the three angels, which are yet to sound!
And the fifth angel sounded, and I saw a star fall from heaven unto the earth: and to him was given the key of the bottomless pit. And he opened the bottomless pit; and there arose a smoke out of the pit, as the smoke of a great furnace; and the sun and the air were darkened by reason of the smoke of the pit. And there came out of the smoke locusts upon the earth: and unto them was given power, as the scorpions of the earth have power. And it was commanded them that they should not hurt the grass of the earth, neither any green thing, neither any tree; but only those men which have not the seal of God in their foreheads. And to them it was given that they should not kill them, but that they should be tormented five months: and their torment was as the torment of a scorpion, when he striketh a man. And in those days shall men seek death, and shall not find it; and shall desire to die, and death shall flee from them. And the shapes of the locusts were like unto horses prepared unto battle; and on their heads were as it were crowns like gold, and their faces were as the faces of men. And they had hair as the hair of women, and their teeth were as the teeth of lions. And they had breastplates, as it were breastplates of iron; and the sound of their wings was as the sound of chariots of many horses running to battle. And they had tails like unto scorpions, and there were stings in their tails: and their power was to hurt men five months. And they had a king over them, which is the angel of the bottomless pit, whose name in the Hebrew tongue is Abaddon, but in the Greek tongue hath his name Apollyon. One woe is past; and, behold, there come two woes more hereafter.
And the sixth angel sounded, and I heard a voice from the four horns of the golden altar which is before God, Saying to the sixth angel which had the trumpet, Loose the four angels which are bound in the great river Euphrates. And the four angels were loosed, which were prepared for an hour, and a day, and a month, and a year, for to slay the third part of men. And the number of the army of the horsemen were two hundred thousand thousand: and I heard the number of them. And thus I saw the horses in the vision, and them that sat on them, having breastplates of fire, and of jacinth, and brimstone: and the heads of the horses were as the heads of lions; and out of their mouths issued fire and smoke and brimstone. By these three was the third part of men killed, by the fire, and by the smoke, and by the brimstone, which issued out of their mouths. For their power is in their mouth, and in their tails: for their tails were like unto serpents, and had heads, and with them they do hurt. And the rest of the men which were not killed by these plagues yet repented not of the works of their hands, that they should not worship devils, and idols of gold, and silver, and brass, and stone, and of wood: which neither can see, nor hear, nor walk: Neither repented they of their murders, nor of their sorceries, nor of their fornication, nor of their thefts.
And after three days and an half the Spirit of life from God entered into them, and they stood upon their feet; and great fear fell upon them which saw them. And they heard a great voice from heaven saying unto them, Come up hither. And they ascended up to heaven in a cloud; and their enemies beheld them. And the same hour was there a great earthquake, and the tenth part of the city fell, and in the earthquake were slain of men seven thousand: and the remnant were affrighted, and gave glory to the God of heaven. The second woe is past; and, behold, the third woe cometh quickly. And the seventh angel sounded; and there were great voices in heaven, saying, The kingdoms of this world are become the kingdoms of our Lord, and of his Christ; and he shall reign for ever and ever. And the four and twenty elders, which sat before God on their seats, fell upon their faces, and worshipped God, Saying, We give thee thanks, O LORD God Almighty, which art, and wast, and art to come; because thou hast taken to thee thy great power, and hast reigned. And the nations were angry, and thy wrath is come, and the time of the dead, that they should be judged, and that thou shouldest give reward unto thy servants the prophets, and to the saints, and them that fear thy name, small and great; and shouldest destroy them which destroy the earth. And the temple of God was opened in heaven, and there was seen in his temple the ark of his testament: and there were lightnings, and voices, and thunderings, and an earthquake, and great hail.
From the books
This answer is drawn from these passages in the Mary Banks Faith Library.