The best introduction to the spirit of St. Thomas is, to my mind, the small book by G. K. Chesterton, St. Thomas Aquinas.  This is not a scholarly work in the proper sense of the word; it might be called journalistic—for which reason I am somewhat chary about recommending it. Maisie Ward, co-owner of the British-American publishing firm which publishes the book, writes in her biography of Chesterton  that at the time her house published it, she was seized by a slight anxiety. However, she goes on to say, Étienne Gilson read it and commented: “Chesterton makes one despair. I have been studying St. Thomas all my life and I could never have written such a book.” Still troubled by the ambiguity of this comment, Maisie Ward asked Gilson once more for his verdict on the Chesterton book. This time he expressed himself in unmistakable terms: “I consider it as being, without possible comparison, the best book ever written on St. Thomas. . . . Everybody will no doubt admit that it is a ‘clever’ book, but the few readers who have spent twenty or thirty years in studying St. Thomas Aquinas, and who, perhaps, have themselves published two or three volumes on the subject, cannot fail to perceive that the so-called ‘wit’ of Chesterton has put their scholarship to shame. . . . He has said all that which they were more or less clumsily attempting to express in academic formulas.” Thus Gilson. I think this praise somewhat exaggerated; but at any rate I need feel no great embarrassment about recommending an “unscholarly” book.
(source: St. Thomas Aquinas and the Thirteenth Century | Josef Pieper)