For Augustine, truth is inseparable from God, and, indeed, this is the view of the entire canon of Scripture. Biblically speaking, we distinguish between two kinds of revelation: natural revelation, truth given to us in the created order (Ps. 19), and supernatural revelation, truth found in the Word of God. Whether we study the physical world and learn how the elements react when combined with one another or study a passage of Scripture, the knowledge we gain finds its source in the Creator Himself.
This is an important principle to remember because we do not often consider ourselves to be studying God’s revelation when we analyze anything other than sacred Scripture. But if God is the maker of all things, then all truth is His truth, and every time a person grasps a truth he betrays his being created in the image of God. Augustine likened the role of divine illumination in human knowledge to light in a darkened room. Were we to find ourselves in a room completely walled off from any outside light, we would have no more awareness of what surrounds us than a blind man, even though there is nothing wrong with our eyes. Just as it takes light in this room to give us knowledge of our surroundings, so too must God illumine His revelation, both natural and special, if we are to gain understanding. Such illumination is not always salvific, for there are many people with true knowledge of the universe who are not servants of the Creator. Nevertheless, that they know anything at all means that God’s revelation in the natural world has penetrated their fallen minds.
Recognizing his dependence upon divine illumination, Augustine penned those famous words: credo ut intelligam, that is, “I believe in order to understand.” With this phrase, Augustine shows us that faith and reason are ultimately inseparable and exist in a reciprocal relationship. We trust authorities like doctors, historians, pastors, employers, computer programmers, lawyers, and others everyday in order to live our lives, but we would not deliberately trust anyone who is untrustworthy. Having been given faith to follow Him, Christians trust in God in order to know the world around them.