P. Diego Ruiz de Montoya's Preface to his Disputations on the Trinity (Part 1)
Commentaria ac Disputationes in Primam Partem Sancti Thomae, De Trinitate, (Lyon, 1625) pg. 1.
Original Latin:
1. The mystery of the Trinity exceeds human capacity. Without faith it would be impossible to find some evidence for it, not to speak of a clear demonstration of it! Even with faith, we are not able to establish some natural proof, nor credibly approve of it by natural reason; but we are only able to soften the difficulty by similarities and to deal with the arguments of heretics.
2. This impossibility is dealt with in disputation 41 and 43. For now it will suffice to seize upon this by Dionysius: “No monad, nor triad, nor number, nor unity, nor productiveness, nor any other existing thing, or thing known, reveals that hiddenness of the Super-Deity, which is above all things, which surpasses every reason and every mind; nor has it a name, or reason; but to those things, it does not give access, but is hidden.” Even though Dionysius wrote similar things about the attributes of the divine essence, still many of these are clearly proved by natural reason. Therefore, within that secret which is inaccessible, we ought to understand that this divinity lies hidden primarily on account of the mystery of the Trinity; although more than a few things (about which, their difficulty is never exhausted by theologians) are revealed regarding the unity of the divine essence and the Trinitarian operations.
3. Therefore, seeing that faith can in no way fight with natural reason, lest the God of both be shown to fight with himself; there are reasons to searched for by which the objections of our adversaries are weakened, and it is manifestly shown that the human intellect is frequently deceived by apparent evidences fighting amongst themselves, even concerning the lowest of things, whether those things which we have among us, or what we touch with our hand, e.g., concerning number and the distinction of the parts of quantity, concerning reality and the distinction of relations, concerning the causes of sickness and its remedies, and finally concerning other innumerable things.
4. Therefore, nothing is able to be demonstrated clearly by natural reason which ought to be disdained as false in divine things (which the authority of God has given to the church by revelation), no matter which arguments move in the opposite direction, even though they seem to manifest apparent evidence. So, Nazianzus: “And let faith lead us rather than reason—But only if you have truly learned the weakness of the latter in matters nearer to you, and have come to know that it is in keeping with reason that you know those things which are above reason, lest you be completely of the earth because you are ignorant even of your ignorance.” But more concerning this is in Disp. Sec. 1.
5. Therefore, one should not desist from the more noble study of learning and defending the mystery of the Trinity, but, one should diligently and strenuously labor in that according to the pattern of the ancient Fathers, chiefly Athanasius, Nazianzens, Basil, Nyssa, Chrysostom, Ambrose, Hilary, and Augustine. But of this labor Nazianzens, Hilary, and Augustine added clear exhortation (referred to after the middle part of section 1 disp. 15). For we will show from the sacred writings and from the doctors of the church that it is most useful and pious to inquire into things by examining them soberly, wisely, and with humility, and with the possibility to find many things which convey some light of faith, and make clear the falsehoods of our adversaries (see disput. 5 section 2). There, we will also note the sins which the Fathers warned us to avoid, when they forbid us to investigate or dispute about the arguments, which we likewise reference in the same disputation (disp. 5 sect. 1).