NECESSITY OF DIVINE REVELATION
Revelation is Strictly Necessary for the Knowledge of Essentially Supernatural Religious Truths
It has long been recognized that there are natural truths about God that can be known by reason alone, but there are also supernatural truths that cannot be known without the aid of divine revelation. It will be shown below that divine revelation is necessary for the attainment of both natural and essentially supernatural truths, but a different kind of necessity applies to each.
In the order of operation or action, an act is said to be strictly necessary when it is indispensable for the attainment of an end. Now, essentially supernatural truths are, by definition, those truths that reason cannot attain on its own simply from its knowledge of the external world. If these truths be not revealed, there is no way for the human mind to know them. Therefore, for the attainment of essentially supernatural religious truths, divine revelation is strictly necessary.
For example, one important supernatural truth that we need to know is our predestination to eternal glory. Based on human reason alone, we would never know that God has actually destined us to a loftier and higher goal (Heaven) than the natural happiness of the present world. St Paul says “That eye hath not seen, nor ear heard, neither hath it entered into the heart of man, what things God hath prepared for them that love him” (1 Cor 2:9). Now, if this truth be not revealed to us, then we would not strive toward it, and fail to attain it. Therefore, for us to attain our supernatural goal, divine revelation is strictly necessary.
Revelation is Morally Necessary even for the Knowledge of Natural Religious Truths
When it comes to the knowledge of natural religious truths, or truths that can be attained by reason alone (such as the knowledge of God’s existence and some of His attributes), divine revelation is not strictly necessary, but it is useful. Now, an act is said to be morally necessary for the attainment of an end if it is useful for the attainment of that end, or if, without it, the end can be attained but not well attained, or is attainable but with great difficulty. Using this definition, it can be said that for the adequate knowledge of natural religious truths, divine revelation is at least morally necessary, although not strictly necessary. The reasons are as follows:
Firstly, the reasoning involved in the task of knowing natural religious truths, such as the knowledge of the nature of the Creator from the nature of the created world, is a long and complicated process requiring time, philosophical skill and education. A divine revelation about these natural religious truths (although attainable solely by reason) is, therefore, very useful. Indeed, very few people have the time, the resources and the energy to engage in the task of pursuing natural religious truths. Without the aid of divine revelation an adequate knowledge of natural religious truths would be attainable only with great difficulty. One can examine, for example, the religious knowledge and practices of pagan peoples, and see that they were marked with gross errors and immorality. Sure, even the most primitive peoples acknowledge the existence of a Supreme Being (God), but they hardly attain a correct notion of God’s essence or nature. Almost all the great pagan religions are either pantheistic or polytheistic, whose gods are often at feud with one another. And most of these pagan religions fail to recognize the spiritual nature of God, which is why they turn to the worship of idols (idolatry). This is also why superstition, magic and obscenity often find a place in their worship. Without divine revelation people hardly ever rise to an adequate understanding of basic religious truths.
Idols (Pagan Rus)
From a painting by Nicholas Roerich, 1910
Image source link: Wikiart.org
Pasht: Lion-headed Egyptian goddess
In Ancient Egypt idolatry took the form of animal worship (zoolatry)
Image source link: Karenswhimsy.com
Without divine revelation pagan worship degenerates into idolatry and polytheism.
This observation is true, not only of primitive and illiterate people, but even of educated people in civilized societies. In fact, none of the great thinkers and philosophers of the civilized world had made a reasonably complete exposition of natural theology or a flawless natural moral code, indicating how weak the human mind is in exploring even those truths that are supposedly within its reach. For example, Plato (428-347 B.C.) recorded a conversation between Socrates and Glaucon, in which Socrates envisioned an ideal State where the male guardians hold wives in common, where the State regulates marriage to produce good offspring the way an animal breeder does, and where children never come to know their mothers but only their nurses, and where deficient or deformed children are then put away in some hidden place (See Plato, The Republic, Book V). Yet, Socrates was a respected philosopher in Ancient Greece! This is what may be expected when reason is allowed to figure moral laws and rules of conduct without the aid of divine revelation. It often results in laws that pay no respect to the dignity of the human person.
Secondly, even if anyone succeeds in discovering the correct principles of natural religion and ethics, his work and opinions would still be inadequate from the standpoint of authority. “Why,” anybody could ask, “should I accept this man’s opinion rather than my own?” Therefore, a supernatural revelation with the stamp of God’s authority is required to ensure a safe and certain knowledge of natural religious truths.
For the reasons stated above Vatican II reaffirms that certain things about God can indeed be known by human reason unaided by revelation, but it is through divine revelation that we know these natural truths "with ease, with solid certitude, and with no trace of error" (Vatican II, Dei Verbum, Chapter 1, #6).