From Summa Conta Gentiles, Book one, Chapter Five, on why it’s fitting for some things to be accepted as revelation (emph. mine: St. Thomas didn’t often use bold typefaces):

“Again, this truth needed to be proposed to man as an object of faith so that he may have truer knowledge of God. For we only know God truly when we believe that he is far above all that man can possibly think of God, for the divine essence surpasses man’s natural knowledge, as stated above (ch. 3). Thus, by the fact that certain things about God are proposed to man which surpass his reason, he is strengthened in his opinion that God is far above what he is able to think.

“Another advantage results from this, namely, the checking of presumption, which is the mother of error. For there are some who presume so far on their wits that they think themselves capable of measuring the whole nature of things by their intellect, namely, thinking all things are true that seem so to them, and false which do not. Accordingly, so that man’s mind might be freed from this presumption and seek the truth humbly, it was necessary that God should propose to man certain things far surpassing his intellect.”