This is the second tool the brothers use to conquer the dragon. The term “testimony” refers to the witness these brothers made concerning the blood of the Lamb in their interactions in daily life—and so links back to the witnesses
of Revelation 11:3 (the same word is used in the Greek). They are able to make this witness because the triumphant and ascendant Christ has poured out his Holy Spirit. Their witness (testimony) concerning the benefits of the blood of the Lamb silences the devil’s accusations before God’s throne.
11 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.