I prayed him much that he would explain to me the similitude of the field, and of the master of the vineyard, and of the slave who staked the vineyard, and of the sakes, and of the weeds that were plucked out of the vineyard, and of the son, and of the friends who were fellow-councillors, for I knew that all these things were a kind of parable. And he answered me, and said, “You are exceedingly persistent with your questions. You ought not,” he continued, “to ask any questions at all; for if it is needful to explain anything, it will be made known to you.”
I said to him, “Sir, whatsoever you show me, and do not explain, I shall have seen to no purpose, not understanding its meaning. In like manner, also, if you speak parables to me, and do not unfold them, I shall have heard your words in vain.” And he answered me again, saying, “Every one who is the servant of God, and has his Lord in his heart, asks of Him understanding, and receives it, and opens up every parable; and the words of the Lord become known to him which are spoken in parables. But those who are weak and slothful in prayer, hesitate to ask anything from the Lord; but the Lord is full of compassion, and gives without fail to all who ask Him.
But you, having been strengthened by the holy Angel, and having obtained from Him such intercession, and not being slothful, why do not you ask of the Lord understanding, and receive it from Him?” I said to him, “Sir, having you with me, I am necessitated to ask questions of you, for you show me all things, and converse with me; but if I were to see or hear these things without you, I would then ask the Lord to explain them.”
Source: The Pastor (or "The Shepherd") (New Advent)