Any account of St. Thomas’s work and accomplishments includes how he “showed that faith and reason were not opposed to one another”. The statement is true, but it runs the risk of being understood in a rationalist sense. To say that faith and reason can never contradict does not mean that one can have a rational basis for everything in the faith. One might be able to prove (and not without difficulty) that there is no contradiction in the doctrine of the Trinity or the hypostatic union or the inspiration of the Scriptures, but absence of contradiction is not the presence of evidence or even justification. Again, “having evidence for X” or “having justification for X” never means (merely) knowing that there is no formal contradiction of X; and so Christianity really does demand that we believe some things with no rational basis or justification.
St. Thomas’s response to this state of affairs was constant throughout his career. Consider an objection that he raises to the claim that “God requires that we believe things beyond reason”:
[I]t is dangerous for man to assent to matters which he cannot judge whether that which is proposed to him be true or false… but a man cannot form a judgment of this kind in matters of faith, since he cannot trace them back to first principles, by which all our judgments are guided. Therefore it is dangerous to believe in such matters.
What rationalist could have said it better? It is obviously impossible to judge somethign to be true if you don’t have that by which it is judged to be true. St. Thomas consistently responds to this sort of objection like this:
Just as man assents to first principles, by the natural light of his intellect, so does a virtuous man, by the habit of virtue, judge aright of things concerning that virtue; and in this way, by the light of faith which God bestows on him, a man assents to matters of faith and not to those which are against faith. Consequently there is no danger or condemnation to them that are in Christ Jesus, and whom He has enlightened by faith.
The appeal is to the light of faith, a distinct habitus that empowers one to judge things as true that cannot be so judged apart from such a light. One has here the simultaneous vindication and scandal to rationalism: on the one hand St. Thomas accepts the truth that one cannot accept the truth of what they cannot judge for themselves, on the other hand he denies that every such power is one that human beings have of themselves (“themselves” is not used in exactly the same way, but we put it like this to show the scandal of the position).