The same thing may be understood from consideration of degrees of intelligibility.* Of two minds, one of which has a keener insight into truth than the other, the higher mind understands much that the other cannot grasp at all, as is clear in the 'plain man' (in rustico), who can in no way grasp the subtle theories of philosophy. Now the intellect of an angel excels that of a man more than the intellect of the ablest philosopher excels that of the plainest of plain men (rudissimi idiotae). The angel has a higher standpoint in creation than man as a basis of his knowledge of God, inasmuch as the substance of the angel, whereby he is led to know God by a process of natural knowledge, is nobler and more excellent than the things of sense, and even than the soul itself, whereby the human mind rises to the knowledge of God. But the Divine Mind exceeds the angelic much more than the angelic the human. For the Divine Mind of its own comprehensiveness covers the whole extent of its substance, and therefore perfectly understands its own essence, and knows all that is knowable about itself; but an angel of his natural knowledge does not know the essence of God, because the angel's own substance, whereby it is led to a knowledge of God, is an effect inadequate to the power of the cause that created it. Hence not all things that God understands in Himself can be grasped by the natural knowledge of an angel; nor is human reason competent to take in all that an angel understands of his own natural ability. As therefore it would be the height of madness in a 'plain man' to declare a philosopher's propositions false, because he could not understand them, so and much more would a man show exceeding folly if he suspected of falsehood a divine revelation given by the ministry of angels, on the mere ground that it was beyond the investigation of reason.*
The same thing manifestly appears from the incapacity which we daily experience in the observation of nature. We are ignorant of very many properties of the things of sense; and of the properties that our senses do apprehend, in most cases we cannot perfectly discover the reason. Much more is it beyond the competence of human reason to investigate all the points of intelligibility in that supreme excellent and transcendent substance of God. Consonant with this is the saying of the Philosopher, that "as the eyes of bats are to the light of the sun, so is the intelligence of our soul to the things most manifest by nature" (Aristotle, Metaphysics I, min. i). To this truth Holy Scripture also bears testimony. For it is said: Perchance thou wilt seize upon the traces of God, and fully discover the Almighty (Job xi, 7). And, Lo, God is great, and surpassing our knowledge (Job xxxvi, 26). And, We know in part (I Cor. xiii, 9). Not everything, therefore, that is said of God, even though it be beyond the power of reason to investigate, is at once to be rejected as false.
1.2 : Of the Author's Purpose
1.4 : That it is an Advantage for the Truths of God, known by Natural Reason, to be proposed to men to be believed on Faith