Lewis sets out in this work to address the philosophical question, are miracles possible? He does not answer the question of the possibility of miracles with the use of historical evidences, but begins his answer by looking to the fundamental worldview of the person. Is the person considering the question a naturalist or a supernaturalist? Does the person considering the question believe that the materials found in the natural order are all that exist—is Nature the whole picture? Or is there some other Reality that supersedes Nature, that is above Nature, that created Nature? Lewis analyzes the differences between naturalism and supernaturalism, and shows that naturalism suffers from internal inconsistency and only supernaturalism can account for the rationality of man’s mind and the intelligibility of the universe. Naturalism also suffers from an inability to account for the morality of humans, for the idea of ought and ought not. In this way, Lewis shows that, since naturalism is irrational and invalid, supernaturalism is the only other reasonable option. Since this is the case, miracles are possible.
After dispensing with naturalism as a coherent philosophical system, Lewis examines the idea of miracle, giving definitions for the term and defining the term’s boundaries. He clearly does not accept the view that miracles are a violation of the laws of nature. Orthodox Christianity certainly does not deny the laws of nature, nor does it deny that order which is found in nature. A miracle, by definition, does not break those laws which are easily observable and which make the universe intelligible. A miracle, Lewis describes, is an interruption into those laws, but the laws of nature take over where the miracle had interrupted. If law A causes effect B, then when miracle A(1) occurs, effect B(2) will take over. In other words, when the Holy Spirit overshadowed Mary to conceive in her womb the baby Jesus, she was, in fact, pregnant, and the laws of nature took over from there.
Lewis proceeds to differentiate between Christianity and Religion by stating that the modern concept of religion is pantheistic. A pantheistic God, Lewis writes, is impersonal, predictable, and easily understood and thereby kept under control. The reality is, the God of the universe, the God that Christ has made known, is King and is alive and is not so easily understood. The pantheistic God of modern religion is not capable of bringing about miracles. In contrast, the God of Christianity, the true God is not only capable of causing miracles—miracles are inevitable.
Lewis takes the time to critique Hume on his objection that miracles are not possible because they are improbable. One can observe a million human deaths and never witness a miracle of resurrection, therefore, miracles of resurrection do not occur. Lewis shows that this proposition is based on the uniformity of nature. But if this principle is questioned, then Hume’s hypothesis no longer is valid. Thus, Lewis states that the criterion for the probability of miracles must not be the uniformity of nature, but instead, the fitness of that miracle to occur in a universe in which God is the ultimate reality. Lewis proceeds to present the miracles of the Christian faith, namely, the Incarnation, the miracles of the Old Testament, and the miracles of Christ culminating in the Resurrection, in order to show their fitness in this universe.
Lewis closes his work by emphasizing that miracles are, by definition, very rare. He writes, “You are probably quite right in thinking you will never see a miracle done” (201). Miracles occur at moments of the most profound spiritual turning points in history.