666 is the number of the second beast in Revelation 13, sent by Satan to deceive those who dwell on earth. The beast is allowed to slay those who refuse to worship the image of the first beast, a fearsome picture of the war that Satan wages against Christ’s bride, the Church. Yet we Christians need not be afraid. The beast and its image and the number of its name are conquered:
And I saw what appeared to be a sea of glass mingled with fire--and also those who had conquered the beast and its image and the number of its name, standing beside the sea of glass with harps of God in their hands. And they sing the song of Moses, the servant of God, and the song of the Lamb, saying, "Great and amazing are your deeds, O Lord God the Almighty! Just and true are your ways, O King of the nations! Who will not fear, O Lord, and glorify your name? For you alone are holy. All nations will come and worship you, for your righteous acts have been revealed." Revelation 15:2-4 ESVIn Christ’s death and resurrection, He defeats Satan, and we can join with our fellow redeemed to sing God’s praises forevermore: “For you alone are holy. All nations will come and worship you, for your righteous acts have been revealed." We need not fear the number of the beast.