John Wesley on Revelation 6:10

And they cried - This cry did not begin now, but under the first Roman persecution. The Romans themselves had already avenged the martyrs slain by the Jews on that whole nation. How long - They knew their blood would be avenged; but not immediately, as is now shown them. O Lord - The Greek word properly signifies the master of a family: it is therefore beautifully used by these, who are peculiarly of the household of God. Thou Holy One and true - Both the holiness and truth of God require him to execute judgment and vengeance. Dost thou not judge and avenge our blood? - There is no impure affection in heaven: therefore, this desire of theirs is pure and suitable to the will of God. The martyrs are concerned for the praise of their Master, of his holiness and truth: and the praise is given him, Rev 19:2, where the prayer of the martyrs is changed into a thanksgiving: Thou holy One and true: "True and right are thy judgments." How long dost thou not judge and avenge our blood? "He hath judged the great whore, and hath avenged the blood of his servants."