Satan; the Devil; the Evil One. From beginning to end of the New Testament he is the Adversary of mankind. We learn much about his temptations and deceptions in the New Testament, as well as how to stand firm against his devices.
John is given a vision of what Christians will endure. Earthly powers empowered by the Evil One are strong and will make war on the saints. Christians can overcome the beast in faithfulness to God. What does it all mean?
And I heard a great voice in heaven, saying, Now is come the salvation, and the power, and the kingdom of our God, and the authority of his Christ: for the accuser of our brethren is cast down, who accuseth them before our God day and night. And they overcame him because of the blood of the Lamb, and because of the word of their testimony; and they loved not their life even unto death. Therefore rejoice, O heavens, and ye that dwell in them. Woe for the earth and for the sea: because the devil is gone down unto you, having great wrath, knowing that he hath but a short time (Revelation 12:10-12).
And I saw as it were a sea of glass mingled with fire; and them that come off victorious from the beast, and from his image, and from the number of his name, standing by the sea of glass, having harps of God. And they sing the song of Moses the servant of God, and the song of the Lamb, saying, “Great and marvellous are thy works, O Lord God, the Almighty; righteous and true are thy ways, thou King of the ages. Who shall not fear, O Lord, and glorify thy name? for thou only art holy; for all the nations shall come and worship before thee; for thy righteous acts have been made manifest” (Revelation 15:2-4).