This verse is the second stanza of the three-verse victory song. It explains the cause of Satan's removal from heaven.
"And they (our brethren) OVERCAME him (the accuser)
OVERCOMERS are a major theme in Revelation. The OVERCOMER's reward is found in Revelation 2:10.
because of the BLOOD OF THE LAMB and
because of the WORD of THEIR TESTIMONY,
It is imperative for a believer to SPEAK of what Jesus Christ did for them. Check it out: Romans 10:9; Psalm 19:14; and 1 Peter 3:15. Compare this to John's view of the TESTIMONY in Revelation 1:9; Revelation 6:9; Revelation 14:12; and Revelation 20:4. That is how important SPEAKING THE WORD of TESTIMONY is.
and they did not love their LIFE even to DEATH.
Being "completely committed" to Jesus Christ says my earthly life is not important compared to my eternal life. Jesus talked about this in Matthew 10:34-39 and Mark 13:9-13. Can you claim and speak these three things today? Why not?