Today is the feast of St. Teresa of Avila, Doctor of the Church. From The Way of Perfection (Chapter 5):
You already know that the first stone of this foundation must be a good conscience and that you must make every effort to free yourselves from even venial sins and follow the greatest possible perfection. You might suppose that any confessor would know this, but you would be wrong: it happened that I had to go about matters of consciences to a man who had taken a complete course in theology; and he did me a great deal of mischief by telling me that certain things were of no importance. I know that he had no intention of deceiving me, or any reason for doing so: it was simply that he knew no better. And in addition to this instance I have met with two or three similar ones.
Everything depends on our having true light to keep the law of God perfectly. This is a firm basis for prayer; but without this strong foundation the whole building will go awry....