By St. Augustine of Hippo, Confessions:
"For it is thou, O Lord, who judgest me. For although no man 'knows the things of a man, save the spirit of the man which is in him,' yet there is something of man which 'the spirit of the man which is in him' does not know itself. But thou, O Lord, who madest him, knowest him completely. And even I--though in thy sight I despise myself and count myself but dust and ashes--even I know something about thee which I do not know about myself. And it is certain that 'now we see through a glass darkly,' not yet 'face to face.' Therefore, as long as I journey away from thee, I am more present with myself than with thee. I know that thou canst not suffer violence, but I myself do not know what temptations I can resist, and what I cannot. But there is hope, because thou art faithful and thou wilt not allow us to be tempted beyond our ability to resist, but wilt with the temptation also make a way of escape that we may be able to bear it. I would therefore confess what I know about myself; I will also confess what I do not know about myself. What I do know of myself, I know from thy enlightening of me; and what I do not know of myself, I will continue not to know until the time when my 'darkness is as the noonday' in thy sight."
From Albert C. Outler, Ph.D.'s Introduction to his translation of St. Augustine's Confessions:
"One does not read far in the Confessions before he recognizes that the term 'confess' has a double range of meaning. On the one hand, it obviously refers to the free acknowledgment, before God, of the truth one knows about oneself--and this obviously meant, for Augustine, the 'confession of sins.' But, at the same time, and more importantly, confiteri means to acknowledge, to God, the truth one knows about God. To confess, then, is to praise and glorify God; it is an exercise in self-knowledge and true humility in the atmosphere of grace and reconciliation."
By St. Bernard of Clairvaux, On Humility and Pride:
"Here is a definition of humility. 'Humility is the virtue by which a man recognizes his own unworthiness because he really knows himself.'"
By St. Angela of Foligno, Instructions:
"Through perseverance in true prayer, divine light and grace increase, and these always make the soul grow deep in humility as it reads, as it has been said, the life of Jesus Christ, God and man. I cannot conceive anything greater than the manifestation of God and self. But this discovery, that is, this manifestation of God and self, is the lot only of those legitimate sons of God who have devoted themselves to true prayer."
By St. Teresa of Avila, Interior Castle:
"I believe we shall never learn to know ourselves except by endeavouring to know God, for, beholding His greatness we are struck by our own baseness, His purity shows our foulness, and by meditating on His humility we find how very far we are from being humble."