See the first post in this series for an explanation and guide.
(1) WHILE then the truth of the intelligible things of God is twofold, one to which the inquiry of reason can attain, the other which surpasses the whole range of human reason, both are fittingly proposed by God to man as an object of belief.i
We must first show this with regard to that truth which is attainable by the inquiry of reason, lest it appears to some, that since it can be attained by reason, it was useless to make it an object of faith by supernatural inspiration.ii
(2) Now three disadvantages would result if this truth were left solely to the inquiry of reason.
(3) One is that few men would have knowledge of God: because very many are hindered from gathering the fruit of diligent inquiry, which is the discovery of truth, for three reasons.
Some indeed on account of an indisposition of temperament, by reason of which many are naturally indisposed to knowledge: so that no efforts of theirs would enable them to reach to the attainment of the highest degree of human knowledge, which consists in knowing God.
Some are hindered by the needs of household affairs. For there must needs be among men some that devote themselves to the conduct of temporal affairs, who would be unable to devote so much time to the leisure of contemplative research as to reach the summit of human inquiry, namely the knowledge of God.
And some are hindered by laziness. For in order to acquire the knowledge of God in those things which reason is able to investigate, it is necessary to have a previous knowledge of many things: since almost the entire consideration of philosophy is directed to the knowledge of God: for which reason metaphysics, which is about divine things, is the last of the parts of philosophy to be studied.iii
Wherefore it is not possible to arrive at the inquiry about the aforesaid truth except after a most laborious study: and few are willing to take upon themselves this labour for the love of a knowledge, the natural desire for which has nevertheless been instilled into the mind of man by God.iv
(4) The second disadvantage is that those who would arrive at the discovery of the aforesaid truth would scarcely succeed in doing so after a long time. First, because this truth is so profound, that it is only after long practice that the human intellect is enabled to grasp it by means of reason. Secondly, because many things are required beforehand, as stated above. Thirdly, because at the time of youth, the mind, when tossed about by the various movements of the passions, is not fit for the knowledge of so sublime a truth, whereas calm gives prudence and knowledge, as stated in 7 Phys. Hence mankind would remain in the deepest darkness of ignorance, if the path of reason were the only available way to the knowledge of God: because the knowledge of God which especially makes men perfect and good, would be acquired only by the few, and by these only after a long time.v
(5) The third disadvantage is that much falsehood is mingled with the investigations of human reason, on account of the weakness of our intellect in forming its judgments, and by reason of the admixture of phantasms. Consequently many would remain in doubt about those things even which are most truly demonstrated, through ignoring the force of the demonstration: especially when they perceive that different things are taught by the various men who are called wise. Moreover among the many demonstrated truths, there is sometimes a mixture of falsehood that is not demonstrated, but assumed for some probable or sophistical reason which at times is mistaken for a demonstration. Therefore it was necessary that definite certainty and pure truth about divine things should be offered to man by the way of faith.vi
(6) Accordingly the divine clemency has made this salutary commandment, that even some things which reason is able to investigate must be held by faith: so that all may share in the knowledge of God easily, and without doubt or error.vii
(7) Hence it is written (Eph. iv. 17, 18): That henceforward you walk not as also the Gentiles walk in the vanity of their mind, having their understanding darkened: and (Isa. liv. 13): All thy children shall be taught of the Lord.
iFrom last time, there are some things we can work out for ourselves, but others which we must take on revelation, i.e. on faith.
iiDon’t panic. We’re starting with that which we can prove by reason. The juiciest arguments will be concrete, scientific, and oh so rational.
iiiTo his great shame, Yours Truly fits into category three. How about you, dear reader? I’ll flatter both of us that, because you regularly stop by here, that you at most suffer as I do, but that you’ll be capable of and have the time to understand the arguments to come.
ivDavid Stove, one of my favorite anti-modern modern philosophers said learning requires two things, libraries and leisure. The library of the internet is practically free, but leisure is harder to come by, particularly as we invent more and more labor-saving devices. Most Westerners now on purpose carry with them everywhere Thinking Suppression Devices so that not even by accident will they philosophize.
vIt is shocking that so many would try to figure out the greatest questions we could possibly ask on their own, without study. Would you try to figure quantum mechanics, the calculus, grammar from scratch on your own without consulting the relevant authorities? No, sir, you would not. So why are you so keen on consulting only your untutored thoughts on, say, whether God exists?
viOnce you are presented with an argument with true premises, a valid conclusion, and which is sound, you have no choice, if you are rational, other than to accept it. Likewise, if an argument you cherish is shown to have false premises, an invalid conclusion, or is shown unsound, you must, if you are rational, you must reject it. Thirdly, many of the arguments on which we rely are not well considered, but carried along habitually or because they are deeply pleasing to us. I used to be an atheist, too, so I know what it’s like. Time for some intense scrutiny.
Update Apropos quotation from Peter Kreeft (start 10:30) on why academics have turned traditionally Catholic colleges and universities away from the Truth. “Smart people are very good at just about everything intellectual, including fooling themselves. Ordinary people aren’t smart enough to fool themselves. They have no place to hide. But academics can create all sorts of excuses and places to hide from themselves.”
viiLike I said, this won’t be our path. We’re going to prove everything.
 iii. 7.