I know a person to whom our Lord wanted to show what a soul in mortal sin was like [Teresa is referring to herself. Cf. Spiritual Testimonies, 20]. That person says that in her opinion if this were understood it would be impossible to sin, even though a soul would have to undergo the greatest trials imaginable in order to flee the occasions. So the Lord gave her a strong desire that all might understand this.
May He give you, daughters, the desire to beseech Him earnestly for those who are in this state, who have become total darkness, and whose works have become darkness also. For just as all the streams that flow from a crystal-clear fount are also clear, the works a soul in grace, because they proceed from this fount of life, in which the soul is planted like a tree, are most pleasing in the eyes of both God and man.
There would be no freshness, no fruit, if it were not for this fount sustaining the tree, preventing it from drying up, and causing it to produce good fruit. Thus in the case of a soul that through its own fault withdraws from this fount and plants itself in a place where the water is black and foul-smelling, everything that flows from it is equally wretched and filthy.
It should be kept in mind here that the fount, the shining sun that is in the center of the soul, does not lose its beauty and splendor; it is always present in the soul, and nothing can take away its loveliness. But if a black cloth is placed over a crystal that is in the sun, obviously the sun’s brilliance will have no effect on the crystal even though the sun is shining on it [Cf. The Book of Her Life, 40:5, Spiritual Testimonies, 52].
O souls redeemed by the blood of Jesus Christ! Understand and take pity on yourselves. How is it possible that in realizing these things you don’t strive to remove the pitch from this crystal? See that if your life comes to an end you will never again enjoy this light.
O Jesus, how sad a thing it is to see a soul separated from this light! How miserable is the state of those poor rooms within the castle! How disturbed the senses are, that is, the people who live in these rooms! And in the faculties, that is, among the custodians, the stewards, and the chief waiters, what blindness, what bad management!
In sum, since the tree is planted where the devil is, what fruit can it bear?
Saint Teresa of Avila
The Interior Castle, I, chap. 2, nos. 2–4
Teresa of Avila, St. 1985, The Collected Works of St. Teresa of Avila, translated from the Spanish by Kavanaugh, K; Rodriguez, O, ICS Publications, Washington DC.