As we’ve seen in previous posts, we need divine revelation because our End is God, and we cannot attain to that End by our own powers. We receive the truths of that revelation with the assent of faith because they cannot be demonstrated by means of demonstration, and because the one who has revealed them is God. But it is not as though God merely said “Believe what I have said” without any justification at all. After all, others make similar claims to divine revelation; why should we believe the Christian faith is unique? St Thomas says in SCG I:6 that God has attested to the truth of revelation by means of miracles:
 Those who place their faith in this truth, however, “for which the human reason offers no experimental evidence,” do not believe foolishly, as though “following artificial fables” (2 Peter 2:16). For these “secrets of divine Wisdom” (Job 11:6) the divine Wisdom itself, which knows all things to the full, has deigned to reveal to men. It reveals its own presence, as well as the truth of its teaching and inspiration, by fitting arguments; and in order to confirm those truths that exceed natural knowledge, it gives visible manifestation to works that surpass the ability of all nature. Thus, there are the wonderful cures of illnesses, there is the raising of the dead, and the wonderful immutation in the heavenly bodies; and what is more wonderful, there is the inspiration given to human minds, so that simple and untutored persons, filled with the gift of the Holy Spirit, come to possess instantaneously the highest wisdom and the readiest eloquence. When these arguments were examined, through the efficacy of the abovementioned proof, and not the violent assault of arms or the promise of pleasure, and (what is most wonderful of all) in the midst of the tyranny of the persecutors, an innumerable throng of people, both simple and most learned, flocked to the Christian faith. In this faith there are truths preached that surpass every human intellect; the pleasures of the flesh are curbed; it is taught that the things of the world should be spurned. Now, for the minds of mortal men to assent to these things is the greatest of miracles, just as it is a manifest work of divine inspiration that, spurning visible things, men should seek only what is invisible. Now, that this has happened neither without preparation nor by chance, but as a result of the disposition of God, is clear from the fact that through many pronouncements of the ancient prophets God had foretold that He would do this. The books of these prophets are held in veneration among us Christians, since they give witness to our faith.
 The manner of this confirmation is touched on by St. Paul: “Which,” that is, human salvation, “having begun to be declared by the Lord, was confirmed to us by them that hear Him: God also bearing them witness of signs, and wonders, and divers miracles, and distributions of the Holy Spirit” (Heb. 7:3-4).
Miracles show us that the Word is true; they attest to the truth of what God has revealed. And it’s not as though these miracles have ceased—as though we are left to wonder whether the miracles recorded in the past are merely fables themselves, so that they would offer no substantiation for the truth. Because, as Aquinas says, miracles still happen:
 This wonderful conversion of the world to the Christian faith is the clearest witness of the signs given in the past; so that it is not necessary that they should be further repeated, since they appear most clearly in their effect. For it would be truly more wonderful than all signs if the world had been led by simple and humble men to believe such lofty truths, to accomplish such difficult actions, and to have such high hopes. Yet it is also a fact that, even in our own time, God does not cease to work miracles through His saints for the confirmation of the faith. [ibid.]
And it’s not as though miracles ceased in the Middle Ages. The healings which occur at Lourdes, or the spectacular miracle of Fatima are just two examples that attest to the truth of the Catholic Faith. So although it is true that we must believe articles of faith for which no demonstrations can be given, and although it is true that we ought to believe them for no other reason than that God has proposed them to us, still He condescends to help us in our weakness by giving us signs that confirm that He has spoken and that His Word is true.