Gregory of Nyssa, in the course of his treatise on Christian perfection, lays out these guidelines for the sort of examination of conscience which should be a regular feature of anyone who wants to make progress in Christian discipleship.
The life of the Christian has three distinguishing aspects: deeds, words and thought. Thought comes first, then words, since our words express openly the interior conclusions of the mind. Finally, after thoughts and words, comes action, for our deeds carry out what the mind has conceived. So when one of these results in our acting or speaking or thinking, we must make sure that all our thoughts, words and deeds are controlled by the divine ideal, the revelation of Christ. For then our thoughts, words and deeds will not fall short of the nobility of their implications.
What then must we do, we who have been found worthy of the name of Christ? Each of us must examine his thoughts, words and deeds, to see whether they are directed toward Christ or are turned away from him. This examination is carried out in various ways. Our deeds or our thoughts or our words are not in harmony with Christ if they issue from passion. They then bear the mark of the enemy who smears the pearl of the heart with the slime of passion, dimming and even destroying the lustre of the precious stone.
On the other hand, if they are free from and untainted by every passionate inclination, they are directed toward Christ, the author and source of peace. He is like a pure, untainted stream. If you draw from him the thoughts in your mind and the inclinations of your heart, you will show a likeness to Christ, your source and origin, as the gleaming water in a jar resembles the flowing water from which it was obtained.
For the purity of Christ and the purity that is manifest in our hearts are identical. Christ’s purity, however, is the fountainhead; ours has its source in him and flows out of him. Our life is stamped with the beauty of his thought. The inner and the outer man are harmonized in a kind of music. The mind of Christ is the controlling influence that inspires us to moderation and goodness in our behavior. As I see it, Christian perfection consists in this: sharing the titles which express the meaning of Christ’s name, we bring out this meaning in our minds, our prayers and our way of life.
This is an excerpt from a treatise on Christian Perfection (PG 46, 283-286) written by St. Gregory, bishop of Nyssa (d. 395AD) and is used in the Roman Office of Readings for Tuesday of the 12th week in ordinary time.