Charles Ellicott Commentary Revelation 6:10

"and they cried with a great voice, saying, How long, O Master, the holy and true, dost thou not judge and avenge our blood on them that dwell on the earth?" — Revelation 6:10 (ASV)

How long...?—Better: Until when. O Master (the word is the correlative of “servant,” see Revelation 6:10), the Holy and True, do You not judge and avenge our blood on those who dwell on the earth?

By a dramatic figure the persecuted and slain ones are represented as crying for retribution on their oppressors. It is not the Christians themselves (Luke 23:34 and Acts 7:60) who cry for vengeance, any more than it was Abel himself who cried from the ground to God: it was the blood of Abel (Genesis 4:10); the earth disclosed her blood and refused to cover her slain. The forgotten or ignored wrongs of generations come forth from oblivion and cry for vengeance.

It is a poetic description, but it is not fiction. The righteous blood shed does fall upon the world in retribution: the laws of God avenge themselves, though the victims do not live to behold the reward of the ungodly. On the epithets Holy and True, see Notes on Revelation 3:7.