Augustine of Hippo
Catena Aurea · Lukasevangelium 18
And he spake a parable unto them to this end, that men ought always to pray, and not to faint; Saying, There was in a city a judge, which feared not God, neither regarded man: And there was a widow in that city; and she came unto him, saying, Avenge me of mine adversary. And he would not for a while: but afterwards he said within himself, Though I fear not God, nor regard man; Yet because this widow troubleth me, I will avenge her, lest by her continual coming she weary me. And the Lord said, Hear what the unjust judge saith. And shall not God avenge his own elect, which cry day and night unto him, though he bear long with them? I tell you that he will avenge them speedily. Nevertheless when the Son of man cometh, shall he find faith on the earth? It follows, And there was a widow in that city.
The widow may be said to resemble the Church, which appears desolate until the Lord shall come, who now secretly watches over her. But in the following words, And she came unto him, saying, Avenge me, &c. we are told the reason why the elect of God pray that they may be avenged; which we find also said of the martyrs in the Revelations of St. John, (Rev. 6:10.) though at the same time we are very plainly reminded to pray for our enemies and persecutors. This avenging of the righteous then we must understand to be, that the wicked may perish. And they perish in two ways, either by conversion to righteousness, or by punishment having lost the opportunity of conversion. Although, if all men were converted to God, there would still remain the devil to be condemned at the end of the world. And since the righteous are longing for this end to come, they are not unreasonably said to desire vengeance.