21 But since I know, beloved brethren, that very many are eager, either on account of the burden or the pain of smarting wrongs, to be quickly avenged of those who act harshly and rage against them, we must not withhold the fact in the furthest particular, that placed as we are in the midst of these storms of a jarring world, and, moreover, the persecutions both of Jews or Gentiles, and heretics, we may patiently wait for the day of (God's) vengeance, and not hurry to revenge our suffering with a querulous haste, since it is written, “Wait upon me, says the Lord, in the day of my rising up for a testimony; for my judgment is to the congregations of the nations, that I may take hold on the kings, and pour out upon them my fury.” The Lord commands us to wait, and to bear with brave patience the day of future vengeance; and He also speaks in the Apocalypse, saying, “Seal not the sayings of the prophecy of this book: for now the time is at hand for them that persevere in injuring to injure, and for him that is filthy to be filthy still; but for him that is righteous to do things still more righteous, and likewise for him that is holy to do things still more holy. Behold, I come quickly; and my reward is with me, to render to every man according to his deeds.” Whence also the martyrs, crying out and hastening with grief breaking forth to their revenge, are bidden still to wait, and to give patience for the times to be fulfilled and the martyrs to be completed. “And when He had opened,” says he, “the fifth seal, I saw under the altar of God the souls of them that were slain for the word of God, and for their testimony; and they cried with a loud voice, saying, How long, O Lord, holy and true, do You not judge and avenge our blood on them that dwell on the earth? And there were given to them each white robes; and it was said unto them that they should rest yet for a little season, until the number of their fellow-servants and brethren is fulfilled, who afterwards shall be slain after their example.”
Source: The Treatises of Cyprian (New Advent)