{They overcame him} (autoi enik(8873)an). First aorist active
indicative of 
ika(935c), the verb used by Jesus of his own victory
( Joh 16:33 ) and about him ( Re 3:21  5:5 ). "The victory of the
martyrs marks the failure of Satan's endeavours" (Swete).
{Because of the blood of the Lamb} (dia to haima tou arniou).
As in  1:5  5:6,9  7:14 . The blood of Christ is here presented
by dia as the ground for the victory and not the means, as by
en in  1:5  5:9 . Both ideas are true, but dia with the
accusative gives only the reason. The blood of Christ does
cleanse us from sin ( Joh 1:29  1Jo 1:7 ). Christ conquered
Satan, and so makes our victory possible ( Lu 11:21f.  Heb
2:18 ). "Thus the Lamb is the true sun(8867)oros (like Michael) of
the New Israel, its parakl(8874)os pros ton patera ( 1Jo 2:1 )"
(Swete). {Because of the Word of their testimony} (dia ton logon
t(8873) marturias aut(936e)). The same use of dia, "because of their
testimony to Jesus" as in John's own case in  1:9 . These martyrs
have been true to their part. {They loved not their life even
unto death} (ouk (8867)ap(8873)an ten psuch(886e) aut(936e) achri thanatou).
First aorist active indicative of agapa(935c). They did resist "unto
blood" (mechris haimatos  Heb 12:4 ) and did not put their own
lives before loyalty to Christ. There is a direct reference to
the words of Jesus in  Joh 12:25  as illustrated also in  Mr
8:35  Mt 10:39  16:25  Lu 9:24  17:33 . Paul's own example is
pertinent ( Ac 21:13  Php 1:20ff. ). Jesus himself had been
"obedient unto death" ( Php 2:8 ). These martyrs seem to be still
alive on earth, but their heroism is proleptically pictured.