Augustine of Hippo — as excerpted in the Catena Aurea on Luke 18:1-8

“(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.”