14. Furthermore, since there is a threefold kind of credible thing according to Augustine : "For some things are believed and at the same time understood, some things are first believed and afterward understood, and some things are believed and never understood, as is the case with human history running through past deeds"; that which is so believed that it can be understood by reason is more credible than that which cannot: but that God is triune is of this kind: therefore, since certain historical facts narrated by authoritative Scripture are credible — for it is not incredible that "Abraham begot Isaac"; indeed it is very credible: so also concerning other similar things — therefore it is credible that God is triune and one.
On the contrary: 1. Everything whose contrary all reason dictates is incredible to reason: but all reason dictates the contrary of this, namely that one thing is really three: therefore it is incredible to reason.
2. Furthermore: Everything whose contrary created nature displays is incredible to reason; but every created nature displays the contrary of this, namely that one thing is multiplied in supposits without the form being multiplied: for in any created nature, when the supposit is multiplied, the form is multiplied: therefore if our intellect is led by the hand through creatures to knowing God whether He exists, as is said in First Corinthians thirteen: We see now through a glass in an enigma: since every created nature has a contrary indication to this truth, that God is triune: it is necessary that this be an incredible truth.
3. Again, everything that is believed is believed either by reason or beyond reason: if therefore that God is triune is a believable truth, then either from reason or beyond reason: but if from reason, then it is no longer meritorious, because "faith has no merit where human reason furnishes proof." If beyond reason: but what is believed by one having the use of reason beyond reason is believed irrationally and is not a believable truth: therefore it is believed irrationally, therefore that God is triune is an incredible truth.
4. Again, everything that is believed is believed either for its own sake or for the sake of another: if therefore that God is triune is a believable truth, then either in this way or in that. If for the sake of another: then it is not the object of right faith itself: if for its own sake: but nothing is lovable for its own sake unless it of itself suffices for the affections: therefore nothing is believable for its own sake unless it is of itself evident to the intellect. But that God is triune is not of itself evident to the intellect: therefore it is not a believable truth.
5. Again, virtue is consonant with nature, because, as Cicero says, and Augustine approves, "virtue is a habit consonant with reason in the manner of nature": therefore what is incredible to natural virtue is incredible to the virtue of faith: but that God is triune is not believable by nature itself: therefore neither is it believable by a virtue superadded to nature.
6. Again, grace is the perfection of nature, and perfection does not conflict with the perfectible but is in harmony with it: if therefore that God is triune is not believable through nature, then neither through superadded grace.
7. Again, "the Creator of nature does nothing contrary to nature as cooperator": therefore the teacher and inspirer of nature does nothing contrary to the natural dictate of reason: if therefore that God is triune is not believable through the natural dictate of reason, then it is not believable through superadded inspiration.
8. Again, the principle of scientific knowledge ought to be the easiest thing to know, as is evident in the principles of demonstrations, which are known to the intellect through themselves: therefore the principle of faithful knowledge ought to be the easiest thing to believe: but that God is triune is not the easiest thing to believe, indeed it is very difficult, as is evident in those who do not yet have faith: therefore it is not the first among believable things: nor is it a middle one nor the last, as is apparent: therefore it is in no way believable.
By these reasons it seems possible to show that God's being triune is not believable as fitting to be believed.
Again, it is shown that it is not believable as owed to be believed.
9. No one is bound to that which he cannot do, because Jerome says: "Let him be anathema who says that God has commanded the impossible"; but to believe that God is triune is not in our power, because having faith is a gift of God: therefore if no one is obligated to that which is not in his power, no one is obligated to believe that.
10. Moreover, if we are obligated to believe this, it is either according to the law of nature, or of Scripture, or of grace. Not according to the law of nature, because that law is impressed upon the hearts of men and is most known to all; but this is a hidden truth, concealing itself from human effort. Not according to the law of Scripture, because this truth was believable before Scripture began: furthermore, if it were believable only on account of Scripture, it would not pertain to every age nor to all persons. Not even according to the law of grace, because faith in this existed before the law of grace began: and moreover, the law of grace is a law that is not burdensome: if therefore believing this is difficult, we are not obligated to it according to the law of grace; nor according to the law of nature nor of Scripture, as has been shown: therefore we are in no way bound to believe it.
11. Moreover, if we are bound to believe it, it is either because it is true, or because it is a truth falling under a precept. Not because it is true, because then by equal reasoning we would be bound to believe every truth: if because it falls under a precept, then either a moral or a sacramental one; not because it falls under a sacramental precept, that is evident: nor because it falls under a moral precept, since all moral precepts are reduced to the ten precepts of the Decalogue, in none of which is it commanded to believe God is triune: therefore we are in no way bound to it.
12. Moreover, if we are bound, it is either because it is a truth seen, or a truth heard, or a truth inspired. Not because it is seen, because no wayfarer has seen this: not because it is heard, because then no one would be bound to believe it except one who had heard it: if because it is inspired: but everyone to whom it is inspired believes: therefore no one is bound except one who believes. But this is false: therefore so is the first premise.
13. Furthermore, I ask what moves a Christian to believe that this is true. If you say that divine Scripture moves you: therefore if divine Scripture did not teach this, you would not believe it: but to the contrary: suppose that the whole of Scripture were burned, the Church and the Christian soul would still not depart from faith in the Trinity: therefore the principal reason moving us to this belief does not reside on the part of Scripture. - Furthermore, if you say that miracles move you: to the contrary: "Faith has no merit where human reason provides proof"; and such faith, which comes from miracles, is rather extorted than voluntary: therefore belief of this kind would not be meritorious. - If you say that grace moves you: to the contrary: no one knows whether he has grace, therefore no one knows whether he ought to believe that truth; but concerning a credible thing, to the belief of which we are bound, we are certain that we ought to believe it: therefore we are not moved to believe this by reason of grace. - If you say that eternal truth itself moves us to believe this; but to the contrary: truth moves to belief in nothing unless it is truth that has been seen: therefore since this truth has not been seen by the soul, it seems that it is moved to believe from some other source than from eternal truth itself.
The question therefore is: if this is a credible truth, by what are we moved to believe it, and by what are we bound to believe it?
CONCLUSION.
That God is triune is a credible truth, because to believe this is fitting, due, and worthy.
I respond: It must be said that that God is triune is a credible truth as being fitting and due and worthy to be believed.
For the understanding of this it must be noted that since this credible truth is the foundation of the entire Christian faith, in order that this foundation may remain unshaken, it has a threefold testimony, through which we are led by the hand, bound, and elevated to believe it. This threefold testimony is considered according to the threefold book, which is the book of creatures, the book of Scripture, and the book of life. The first book gives efficacious testimony, the second gives more efficacious testimony, and the third most efficacious.
For the first book, which is the book of the creature, which I therefore call first because it is first presented to our senses, gives a twofold testimony, so that in the mouth of two witnesses every word may stand . For every creature is either a vestige of God only, as is corporeal nature, or is an image of God, as is intellectual creature. Each of these testifies to the Trinity, but that which holds the character of a vestige, as it were from afar. For every creature has mode, species, and order, or unity, truth, and goodness, or measure, number, and weight: which by appropriation correspond to the trinity of persons and through which it is testified that God is triune. And this is what Augustine says in the book of Eighty-Three Questions: "Everything that exists has one thing by which it subsists, another by which it is distinguished, another by which it is fitting. Therefore the whole of creation shows its threefold cause: by which it exists, and by which it is this particular thing, and by which it is in harmony with itself: but we call the cause of the creature, that is, its author, God. Therefore there must be a Trinity, than which perfect reason can find nothing more excellent, more intelligent, and more blessed." From this Augustine shows that the creature holds the character of a vestige, which testifies that God is triune.
But that creature which holds the character of an image, namely the intellectual creature, testifies that God is triune as it were from nearby, because an image is an expressed likeness. For the intellectual creature has memory, understanding, and will, or mind, knowledge, and love: mind after the manner of a parent, knowledge after the manner of offspring, love after the manner of a bond proceeding from both and connecting both; for the mind cannot fail to love the word which it generates. In these, moreover, not only is origin and emanation observed, through which there is distinction in them, but also equality and consubstantiality and inseparability, from which by express testimony it is proclaimed that God is triune. For since He is spirit and intellect, He cannot lack a begotten Word and a proceeding Love, in which there is distinction by reason of the origin and emanation of one from another, together with equality and consubstantiality and inseparability. And this is what Augustine intends to establish in the ninth book of On the Trinity to the end, namely how through the created image testimony is rendered to the eternal Trinity.
Now this twofold testimony of the book of nature was efficacious in the state of nature as created, when neither was that book obscure nor had the eye of man grown dim. But when through the sin of man the eye grew dim, that mirror became enigmatic and obscure, and the ear of interior understanding became deaf to hearing that testimony. And therefore divine providence dispensatively provided the testimony of another book, namely the book of Scripture, which indeed was produced according to divine revelation, which never has been lacking nor will be lacking from the beginning of the world until the end.
Now this book testifies in a twofold manner that the Trinity exists, according to its twofold part: in the Old Testament indeed it testifies implicitly, but in the New Testament it testifies explicitly.