If we remember nothing else from Descartes:
"I fall into error because my God-given ability to judge the truth is not infinite." -- Descartes, Meditations on First Philosophy, Meditation IV.
"It's clear to me that there is more reality in an infinite than in a finite substance and hence that my grasp of the infinite must somehow be prior to my grasp of the finite--my understanding of God prior to my understanding of myself. For how could I understand that I doubt and desire, that I am deficient and imperfect, if I didn't have the idea of something more perfect to use as a standard of comparison?" -- Descartes, Meditations on First Philosophy, Meditation III.
"That is the essential nature of the learned life as I see it. But it has indirect values which are especially important today. If all the world were Christian, it might not matter if all the world were uneducated. But, as it is, a cultural life will exist outside the Church whether it exists inside or not. To be ignorant and simple now...would be to throw down our weapons, and to betray our uneducated brethren who have, under God, no defence but us against the intellectual attacks of the heathen. Good philosophy must exist, if for no other reason, because bad philosophy needs to be answered. The cool intellect must work not only against cool intellect on the other side, but against the muddy heathen mysticisms which deny intellect altogether. Most of all, perhaps, we need intimate knowledge of the past. Not that the past has any magic about it, but because we cannot study the future, and yet need something to set against the present, to remind us that the basic assumptions have been quite different in different periods and that much which seems certain to the uneducated is merely temporary fashion. A man who has lived in many places is not likely to be deceived by the local errors of his native village; the scholar has lived in many times and is therefore in some degree immune from the great cataract of nonsense that pours from the press and the microphone of his own age. " -- C.S. Lewis, The Weight of Glory.
"My central claim is that to flourish as intellectual beings, to grasp truths essential for our living full and happy lives, we must also flourish as emotional and moral beings. For as we have seen, if our lives are marked by deep, ongoing concerns, we will be moved by various circumstances to emotions and virtuous behaviors that in turn equip us to think in ways we could not otherwise think and to grasp truths we could not grasp were we lacking in these traits. But whether these traits become a deeply embedded part of our character is, in part, up to us. How we respond to adversity, and the affect it has on our character and our thinking, is a matter over which we have some control. The Christian tradition, following Scripture, has also taught, however, that we are not alone in our efforts to cultivate life-characterizing concerns and the virtuous emotions and behavior that stem from them; God is ready to assist us. We can hardly do better than to recall the words of James: 'If any of you is lacking in wisdom, ask God, who gives to all generously and ungrudgingly, and it will be given you.'" -- W. Jay Wood, Epistemology: Becoming Intellectually Virtuous.
"All that's left is to explain how I have gotten my idea of God from Him...the idea is innate in me, like my idea of myself. It's not at all surprising that in creating me God put this idea into me, impressing it on His work like a craftsman's mark (which needn't be distinct from the work itself). The very fact that it was God who created me confirms that I have somehow been made in His image or likeness and that I grasp this likeness, which contains the idea of God, in the same way that I grasp myself. Thus, when I turn my mind's eye on myself, I understand, not just that I am an incomplete and dependent thing which constantly strives for bigger and better things, but also that He on whom I depend has all these things in Himself as infinite reality rather than just as vague potentiality and hence that He must be God. The whole argument comes down to this: I know that I could not exist with my present nature--that is, that I could not exist with the idea of God in me--unless there really were a God. This must be the very God whose idea is in me, the thing having all of the perfections that I can't fully comprehend but can somehow reach with thought, who clearly cannot have any defects. From this, it's obvious that He can't deceive--for, as the natural light reveals, fraud and deception arise from defect. But before examining this more carefully and investigating its consequences, I want to dwell for a moment in the contemplation of God, to ponder His attributes, to see and admire and adore the beauty of His boundless light, insofar as my clouded insight allows. As I have faith that the supreme happiness of the next life consists wholly of the contemplation of divine greatness, I now find that contemplation of the same sort, though less perfect, affords the greatest joy available in this life." -- Descartes, Meditations on First Philosophy, Meditation III.
"Your intellectual life is important according to [Aristotle, Augustine, Thomas Aquinas, and other philosophers of the ancient and medieval tradition], for the simple reason that your very character, the kind of person you are and are becoming, is at stake. Careful oversight of our intellectual lives is imperative if we are to think well, and thinking well is an indispensible ingredient in living well. According to this tradition, only by superintending our cognitive life (the way, for example, we form, defend, maintain, revise, abandon and act on our beliefs about important matters) can we become excellent as thinkers and, ultimately, excellent as persons. If we fail to oversee our intellectual life and cultivate virtue, the likely consequence will be a maimed and stunted mind that thwarts our prospects for living a flourishing life... A vicious moral character can undermine good thinking just as effectively as some physical debility. The two-way causal connection between right thinking and right morality, between the intellectual and moral virtues, is a prominent motif that runs through many religious tradition; it is also attested by common sense. Arrogance, dishonesty, pride, pugnacity, laziness, and many other vices undermine our ability to think well and to pursue the truth." -- W. Jay Wood, Epistemology: Becoming Intellectually Virtuous.
"In the last few days, I've gotten used to drawing my mind away from the senses. I've carefully noted that I really grasp very little about physical objects, that I know much more about the human mind, and that I know even more about God. Thus, I no longer find it hard to turn my thoughts away from things of which I can have mental images and toward things completely separate from matter, which I can only understand. Indeed, I have a much more distinct idea of the human mind, insofar as it is just a thinking thing that isn't extended in length, breadth, or depth and doesn't share anything else with physical objects, than I have of physical objects. And, when I note that I doubt or that I am incomplete and dependent, I have a clear and distinct idea of a complete and independent entity: God. From the fact that this idea is in me and that I who have the idea exist, I can clearly infer both that God exists and that I am completely dependent on Him for my existence from moment to moment. This is so obvious that I'm sure that people can't know anything more evidently or certainly. And it now seems to me that, from the contemplation of the true God in whom are hidden all treasure of knowledge and wisdom, there is a way to derive knowledge of other things." -- Descartes, Meditations on First Philosophy, Meditation IV.