Richard Hays proposes the follow explanation of the title “faithful witness,” applied to Jesus in Revelation 1:5 (Revelation and the Politics of Apocalyptic Interpretation, 78-79):

“‘the testimony of Jesus’ must include the memory or message of Jesus’ own faithful suffering and death. This is suggested first of all by the interesting fact that the martyr Antipas in Pergamum is described as ho martus mou ho pistos mou (2:13) – precisely echoing Revelation’s programmatic description of Jesus Himself as ho martus ho pistos (1:5). It is likewise noteworthy that the martyred souls in Revelation 6:9 are said to have been slaughtered (esphagmenon) on account of their testimony – precisely the same verb used to describe the identity of the slaughtered Lamb in 5:6, 9, 11.”

Hays adds, “Here is an unmistakable statement that the ‘testimony’ that conquers evil is not merely a verbal message; instead, it is an embodied testimony, enacted through a confession that refuses the way of violence and undergoes death, just as Jesus did, at the hands of earthy powers.” 

Jesus conquers, as John’s gospel says, by being lifted on the cross and drawing all men to Himself (John 12:32-33; 16:33), and the saints follow Him in His way of victory.