What are the Three Angel's (of Revelations) Messages?
Key Verse:  And I saw another angel fly in the midst of heaven, having the everlasting gospel to preach unto them that dwell on the earth, and to every nation, and kindred, and tongue, and people.  [Revelation 14:6]

In Revelation the 14th chapter, we find three angels' messages.  It is delivered to them that dwell on the earth, and it is given to every nation, kindred, language and people.  It is our duty to help spread these messages.

The first angel's message is found in the seventh verse.  From the key verse, we can see that this angel presents the everlasting gospel.  It is our job, as well, to spread the wonderful message of salvation that has come to us through Jesus Christ our Lord.  The First Angel's message continues with this statement:
Saying with a loud voice, Fear God, and give glory to him; for the hour of his judgment is come: and worship him that made heaven, and earth, and the sea, and the fountains of waters.  [Revelation 14:7]
We are told "with a loud voice" to fear God.  This does not mean that we should be afraid of God but rather to give Him respect, honor and glory.  He is omnipotent or ever powerful.  We are told that the hour of His judgement is come.  His Son, the Lord Jesus Christ, will do the judging when He returns to catch up His saints at the first resurrection.  We must prepare ourselves for Jesus's return.  We are told to worship the Father who made the heaven, the earth, the sea, and fountains of waters.

The second angel then comes onto the scene and cries that Babylon is fallen.  
And there followed another angel, saying, Babylon is fallen, is fallen, that great city, because she made all nations drink of the wine of the wrath of her fornication.   [Revelation 14:8]
Babylon is found in the workings of Satan who makes God's truth into lies.  He works through the Beast power that is found in the previous chapter (Revelation 13).  Babylon is also repesented by "that great city" which made all nations drink of the wine of the wrath of her fornication.  Satan has deceived many people, and these people then teach other peoples, nations and in all languages Satan's untruths.  If a group is not teaching according the truth of God's Word, then they are a part of this great city or Babylonian teachings.  We read in Isaiah the following:  
To the law and to the testimony: if they speak not according to this word, it is because there is no light in them.   [Isaiah 8:20]
The third angel follows the other two, and pronounces with a loud the following message:  
And the third angel followed them, saying with a loud voice, If any man worship the beast and his image, and receive his mark in his forehead, or in his hand.  The same shall drink of the wine of the wrath of God, which is poured out without mixture into the cup of his indignation; and he shall be tormented with fire and brimstone in the presence of the holy angels, and in the presence of the Lamb: The same shall drink of the wine of the wrath of God, which is poured out without mixture into the cup of his indignation; and he shall be tormented with fire and brimstone in the presence of the holy angels, and in the presence of the Lamb:   [Revelation 14:9-11]
The mark of the Beast is blasphemy.  That mark is received by blaspheming God.  When a person teaches and goes against God's Truth and performs it knowingly, that person receives the mark of the beast in his/her hand.  When a person reasons against God's truth knowingly, he/she receives that mark in the forehead.  The wrath of God that will come upon them is the seven last plagues.  
And the temple was filled with smoke from the glory of God, and from his power; and no man was able to enter into the temple, till the seven plagues of the seven angels were fulfilled.  And I heard a great voice out of the temple saying to the seven angels, Go your ways, and pour out the vials of the wrath of God upon the earth.  [Revelation 15:8-16:1]
The seven last plagues will come upon the earth after the reaping phase of Christ's second coming, and will proceed until the second phase of His second coming, the battle of Armaggedon.  It remains our job to warn the people about this mark, so that the will not blaspheme God by going against His Word.  We need to tell them to come out of Babylon.
And I heard a great voice out of the temple saying to the seven angels, Go your ways, and pour out the vials of the wrath of God upon the earth.  For all nations have drunk of the wine of the wrath of her fornication, and the kings of the earth have committed fornication with her, and the merchants of the earth are waxed rich through the abundance of her delicacies.  And I heard another voice from heaven, saying, Come out of her, my people, that ye be not partakers of her sins, and that ye receive not of her plagues.  For her sins have reached unto heaven, and God hath remembered her iniquities.  Reward her even as she rewarded you, and double unto her double according to her works: in the cup which she hath filled fill to her double.  How much she hath glorified herself, and lived deliciously, so much torment and sorrow give her: for she saith in her heart, I sit a queen, and am no widow, and shall see no sorrow. Therefore shall her plagues come in one day, death, and mourning, and famine; and she shall be utterly burned with fire: for strong is the Lord God who judgeth her.  And the kings of the earth, who have committed fornication and lived deliciously with her, shall bewail her, and lament for her, when they shall see the smoke of her burning, Standing afar off for the fear of her torment, saying, Alas, alas that great city Babylon, that mighty city! for in one hour is thy judgment come.   [Revelation 18:2-10]  (Emphasis Added)