They overcame 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. (Rev. 12:11)The antecedent of “they” is “our brothers.” The antecedent of “him” is “Satan.” The spiritual weapon is the blood of the Lamb. The Lamb is the Lord Jesus Christ. Rephrasing the sentence by substituting nouns for pronouns, we have: “Our brothers overcame Satan by the blood of the Lord Jesus Christ.”
The blood of Christ is our salvation, our forgiveness, liberation from sin, redemption, and continual cleansing.
…and from Jesus Christ, who is the faithful witness, the firstborn from the dead, and the ruler of the kings of the earth. To him who loves us and has freed us from our sins by his blood, and has made us to be a kingdom and priests to serve his God and Father – to him be glory and power forever and ever! Amen. (Rev. 1:5-6)This is all the direct work of the Lord Jesus Christ.
God presented him as a sacrifice of atonement, through faith in His blood. He did this to demonstrate his justice, because in his forbearance he had left the sins committed beforehand unpunished. (Rom. 3:25)
Since we have now been justified by His blood, how much more shall we be saved from God’s wrath through him! (Rom. 5:9)
For you know that it was not with perishable things such as silver or gold that you were redeemed from the empty way of life handed down to you from your forefathers, but with the precious blood of Christ, a lamb without blemish or defect. (1 Pet. 1:18-19)
But if we walk in the light, as he is in the light, we have fellowship with one another, and the blood of Jesus, His Son, purifies us from all sin. (1 John 1:7)
In Revelation 12, the brothers overcame Satan by that same blood that saved them. Here the blood is a weapon, linked with “the word of their testimony.” “The blood of the Lamb” is not just a phrase to say. It is the death of the Lord Jesus Christ that overcomes, not the phraseology. Hebrews 2:14: “Since the children have flesh and blood, He too shared in their humanity so that by His death He might destroy him who holds the power of death – that is, the devil.”
We should focus on the second phrase: “so that by his death [the blood of the Lamb], he might destroy him who holds the power of death.”