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?
(lib. ii. qu. 45.) Our Lord utters His parables, either for the sake of the comparison, as in the instance of the creditor, who when forgiving his two debtors all that they owed him was most loved by him who owed him most; or on account of the contrast, from which he draws his conclusion; as, for example, if God so clothe the grass of the field, which to-day is, and tomorrow is cast into the oven, shall he not much more clothe you, O ye of little faith. So also here when he brings forward the case of the unjust judge.