Three, this Art is most subtle
My son, "as humans are composed and constituted of sensual nature and intellectual nature, some have subtlety of the senses, others have intellectual subtlety (Lib. Contemp. Vol. 2. cap. 215.) and others have both, as did the philosophers of antiquity. And since the philosophers treated of nature both universally and in particular, they had subtle knowledge of things both sensual and intellectual. (ibid.) To satisfy these three kinds of persons, I provided an Art and Science to render the mind as subtle and ingenious as possible, in sensual matters, intellectual matters and matters both sensual and intellectual. And so I composed the second volume of the Book of Contemplation using the five sensual senses and the five intellectual senses because these are instruments with which the intellect can achieve both sensual and intellectual subtlety. "And those who seek first to have subtle knowledge of general things from which they descend to specific sensual things cannot achieve as much subtlety as those who begin with sensual things and then rise to subtle knowledge of a general nature (because an intellect that begins with generalities must then descend to sensual things, whereas an intellect that begins with sensual things rises aloft to intellectual things) and thus the philosophers of former times were deceived in many respects as compared to the Teachers who treated of Philosophy and Theology in a perfect and orderly way because they raised their intellect from lower matters to make it subtle in matters of a higher order. (ibid.)
And this is why, in the Comment on the Demonstrative Art, I gave you a prime, supremely universal rule for elevating your intellect to great subtlety in its rise from the lowest degree in the sensual matters of Philosophy, to the loftiest degree in the intellectual subjects of Theology. I taught the very same doctrine in the Book on the Ascent and Descent of the Intellect. And since no one can possibly ascend from the lowest to the highest degree of Subtlety in the subtlest of Truths without a perfect knowledge of the Transcendent Points (that I discussed in the Book of Demonstrations, and expounded clearly and at length in rule eight of Ars Inventiva), heaven enlightened me and revealed the nature and use of these Points that can also serve to detect any error in demonstrations made with natural science by ancient and modern philosophers who had no notion at all of these points.
My son, the supreme Point of all these Points is in Supernatural Faith and Supernatural Reason. Now as the created human intellect, being finite, cannot transcend finite being and attain infinite Being through merely natural power, infinite Being, through grace, wanted to give the intellect an instrument for transcending its natural confines so as to know the supernatural, infinite object, wherein lies the final purpose for which it was primarily created by God: and this is why in the Great Book of Contemplation (Lib. Contempl. Vol.3.Lib.4.Dist.36.cap.238. I placed the Tree of Faith and Reason, and in Figure S, namely the Figure of the Rational Soul, I placed the Red Quadrangle, which stands for faith, and in Lib. Mirand. Demon.2. cap.27.fol.50. I described what a Supernatural Demonstration is: "whereas the Philosophers of old did not investigate the truth with faith, but through reason alone, it follows that their science, in their time, was not worth as much as the science we have now; (Lib. Contempl. Vol. 3. Lib. 5. cap. 364.) because as the Philosophers of old had a way and a means to be subtle through their knowledge of the five universal generalities and the ten predicates, in which all of philosophical subtlety consists, likewise our Scientists and Teachers have a way and a means to be subtle in Theology, because of their faith and of their knowledge of the Soul's nature, virtues and qualities. Lib. Contempl. Vol. 2. Lib. 3. cap. 215.
Therefore, my Son, you must learn my Art, and above all the topic of the Transcendent Points and the way of making supernatural Demonstrations; and learn this not through mere speculation, but through experience and by following what I taught in the abovementioned chapter of Lib. Mir. Dem. and in the chapter following it, and you will know without doubt that the said Art and Work are subtle in the highest degree; "this Art and this Work were to me a source of great sensual and intellectual toil and peril, as a great weight injures and destroys the back of a beast of burden, likewise, on account of its length and subtlety and many new reasons, I sustained much sorrow, toil and peril and bore many insults and much contempt etc.; so that I often felt that I was about to perish in this Book of Contemplation because of my great and pitiful fragility and because of the protracted continuation and great subtlety of this Work. (Lib. Contempl. Vol. 3. Lib. 5. cap. 366. p. 4.)