May everyone learn to know himself—by another in no wise is one known—although the defenses of self-love are so strong that very few persons, if any at all, break through to a knowledge of their own selves.
Under no other teacher or guide than God alone, the builder of man, will it ever be granted to see the secrets of the human heart. For as He created man, so He knows all the headwaters of his cunning and the source whence they come. All of which Jeremiah signified by the words [17:9]: “Who can know it?” doubtless not supposing that any one would venture to avouch that he had knowledge of it, except the God who fashioned it. Hence, at once, he adds: “I, the Lord, who search the heart and try the reins.”
From the Lord God, therefore, the Creator of man, is the knowledge of man to be sought, no less than the knowledge of Himself, though for different reasons. The knowledge of God is denied to our understanding because of its feebleness and His glory and splendor, but the knowledge of man, because of his boldness and readiness in lying and dissembling, as has been said.*
“Know Thyself”? Socrates, that’s not possible. We don’t know who or what we are until God reveals it to us. Self love blinds us so thoroughly that we can’t see clearly enough to know anything until, like Paul, after his experience on the road to Damascus, God opens our eyes.
*The Latin works of Huldreich Zwingli, Volume 3. (C. N. Heller, Ed.) (p. 76). Philadelphia: Heidelberg Press.