Revelation 12:11 - And they overcame him (the devil) by the blood of the
Lamb, and by the word of their testimony; and they loved not their lives
unto the death.
The Blood of the Lamb defeats the devil for it refers to the sacrifice for
our sins on the cross of Calvary. The Lamb is the Lord Jesus Christ who
received the wrath of God and paid the penalty as our substitute. John the
Baptist called Jesus "the Lamb of God who takes away the sin of the world". (John 1:29)
The word of their testimony is: Jesus is Lord, and God has raised him from
the dead. (Romans 10: 9-10).
Even in the face of death, they did not cling to their earthly lives. Their
commitment to Christ was real. In this context, "they" refers to believers
during the Tribulation. But it should also apply to us as believers today.