“For the accuser of our brothers has been thrown down, who accuses them day and night before our God. And they have conquered him by the blood of the Lamb and by the word of their testimony, for they loved not their lives even unto death” (Revelation 12:10-11, ESV).
Some people try to turn the source of evil in the world, Satan, the devil, into a fairy tale. But, the Bible makes it clear that he exists and that he hates those who have been saved by the blood sacrifice of Jesus dying on the cross. He hates Christians so much that he accuses them before God 24/7.