Faith

"O blessed faith, you are certain but you are also obscure. You are obscure because you make us believe truths revealed by God Himself, and which transcend all natural light. Your excessive light, radiance of the divine truths, becomes for me thick darkness because the greater overwhelms the lesser, even as the light of the sun overwhelms all other lights and even exceeds my power of vision....Make me comprehend, O Lord, that to be joined in union with You I must not walk by understanding, neither may I lean upon experience or feeling or imagination, but I must believe in Your infinite Being, which is not perceptible to my understanding." --- St. John of the Cross

"My intellect does not need the concurrence of my will to believe that two and two make four. The truth is evident and I see it. In the case of divine truths, on the contrary, my intellect remains free to give its assent or not, simply because these truths are not evident to me; and I believe only because I will to believe. In the case of natural truths that I can verify, such as mathematical truths, my adherence to them depends upon the power of my intellect: the deeper my knowledge and comprehension of them, the stronger my conviction. But in the presence of supernatural truths, my adherence depends upon the power of my will: the intellect is moved by the will. A free upright will, which loves its God, fully believes all that He reveals, not with a cold acceptance, but with a loving adherence which involves all the powers of the soul.

However, since evidence is lacking, doubt may always arise in the mind, and I should not be astonished at this. It is natural for the human intellect to doubt what it does not see and does not understand. Sometimes doubts are caused by ignorance, in which case we have a duty to seek further instruction; but at other times they will be mere temptations which must be overcome by an act of the will: Lord, I believe because I want to believe; I believe, even if I am in darkness, if I cannot see or understand; I believe solely on your word." --from Divine Intimacy #242 (p. 723 in the one volume)