Actually, St. Thomas never said this. It is a misquote from ST II-II, 1, 5, Reply to Obj. 1:"Unbelievers are in ignorance of things that are of faith, for neither do they see or know them in themselves, nor do they know them to be credible. The faithful, on the other hand, know them, not as by demonstration, but by the light of faith which makes them see that they ought to believe them, as stated above (4, ad 2,3)."- http://newadvent.org/summa/3001.htm#article5The actual quote is quite different from from the one attributed to him in its meaning.
If only St. Thomas had actually said that. I've NEVER seen anyone actually cite a source for this dictum, and it seems to fly in the face of the medieval "fides quaerens intellectum."Faith does seek an explanation...we just know that the explanation can never be fully grasped by our intellect.