Then I heard a loud voice in heaven say: “Now have come the salvation and the power and the kingdom of our God, and the authority of his Messiah. For the accuser of our brothers and sisters, who accuses them before our God day and night, has been hurled down. They triumphed over him by the blood of the Lamb and by the word of their testimony; they did not love their lives so much as to shrink from death.
Revelation 12:10-11
We generally think of Satan as a tempter looking for ways to keep us from Christ. Or to cause us to stumble in our walk with Christ. But here he is pictured as one who accuses us before God. Jesus elsewhere is pictured as our Advocate (1 John 2:1), or defense attorney. Here, Satan is pictured on the other side of the heavenly courtroom as the prosecuting attorney.
And in this courtroom scene, we find that we are able to overcome the accuser with two pieces of evidence. The first is the blood of the Lamb, the blood that washes away my sin. The second piece of evidence presented in my defense is my testimony. Representing a life triumphs by the blood of the Lamb and the presence of the Holy Spirit. Regardless what Satan may do, or accuse us of, we have victory over him. Not because of ourselves, but because of what Jesus did for us, and is doing in us.