Someone wrote me to ask that question. I thought the answer might be of more general interest.
To answer your questions regarding Holy Scripture and the use of the word “supernatural,” let me first address what nature and supernature are. First, everything that is comes from God. God is called “the author of the natural and the supernatural.” From the point of view of God, nothing is “supernatural,” since nothing is above his nature. The terms are relative to the human point of view. Certain things are natural to us, certain things supernatural. For that matter, angels, whose nature is higher than ours are called “praeternatural” from our point of view (Latin praeter means “beyond” or “more than”).
What is natural to us is what we are born with (Latin natus = “born,” as in Hodie Christus natus est — “Christ is born today”). The powers that we have at our conception and birth are natural to us. In baptism, we are elevated to the life of grace. We are thereby divinized and given powers that are not natural to us. They are above our natures. We therefore call them “supernatural.”
When it comes to revelation, we can consider that God reveals himself in two modes, corresponding to the life of nature and the life of grace (supernature) in man. Naturally, God reveals himself through his creation, as Saint Paul says: “For the invisible things of him, from the creation of the world, are clearly seen, being understood by the things that are made; his eternal power also, and divinity…” (Rom. 1:20). We can use our natural reason to arrive at the existence of God from creation, as Saint Thomas does in the famous “five proofs” of his Summa Theologiae.
Vatican I teaches, in its first canon on revelation, that “If anyone says that the one, true God, our Creator and Lord, cannot be known with certainty from the things that have been made, by the natural light of human reason: let him be anathema.”
But, over and above our natural knowledge of the Creator, there is the knowledge that we derive from supernatural revelation — that is, a revelation beyond the mere natural capacities of man. This revelation comes to us through Holy Scripture and Apostolic tradition. It is distinguished by Vatican I as “divine revelation,” whereas the merely natural knowledge of God is called “by the natural light of human reason.”