“Remove from you,” says he, “grief; for she is the sister of doubt and anger.” “How, sir,” say I, “is she the sister of these? For anger, doubt, and grief seem to be quite different from each other.” “You are senseless, O man. Do you not perceive that grief is more wicked than all the spirits, and most terrible to the servants of God, and more than all other spirits destroys man and crushes out the Holy Spirit, and yet, on the other hand, she saves him?” “I am senseless, sir,” say I, “and do not understand these parables.
For how she can crush out, and on the other hand save, I do not perceive.” “Listen,” says he. “Those who have never searched for the truth, nor investigated the nature of the Divinity, but have simply believed, when they devote themselves to and become mixed up with business, and wealth, and heathen friendships, and many other actions of this world, do not perceive the parables of Divinity; for their minds are darkened by these actions, and they are corrupted and become dried up.
Even as beautiful vines, when they are neglected, are withered up by thorns and various plants, so men who have believed, and have afterwards fallen away into many of those actions above mentioned, go astray in their minds, and lose all understanding in regard to righteousness; for if they hear of righteousness, their minds are occupied with their business, and they give no heed at all. Those, on the other hand, who have the fear of God, and search after Godhead and truth, and have their hearts turned to the Lord, quickly perceive and understand what is said to them, because they have the fear of the Lord in them. For where the Lord dwells, there is much understanding. Cleave, then, to the Lord, and you will understand and perceive all things.”
Source: The Pastor (or "The Shepherd") (New Advent)