I had always Gilson described as being a sort of Christian existentialist (people felt the need to add ‘Christian’ because figures like Sartre made their atheism such an important part of both their public image and the problem they attempted to solve). It took me a while to see it until I then read a bit of Hans Urs Von Balthasar, another Catholic thinker (better known as a theologian than a philosopher, though the difference feels hazy to me). Balthasar is a German and Gilson is French, but in terms of how their tendencies towards a sort of existentialism played out, Gilson is very much in the Heidegger mode, concerned with capital ‘B’ Being, whereas Von Balthasar has Sartre’s concern with freedom.
Gilson is attempting to reassert a sort of primacy for beauty. In. formulation of Being, Beauty, and Truth, many times, religious thinkers will put Beauty to use in the service of helping people experience the other two, especially Truth. Gilson seems to have Truth and Beauty emanate more or less equally from Being.
A lot of what he writes in The Arts of the Beautiful seemed to miss the point, to me. He made a mention of something resembling Stendhal Syndrome, and this helped confuse me, because he is not writing for the person who experiences art, but only about making art (in fact, his main point is that art is not a form of knowing, but or making; which doesn’t really make sense for the viewer, I would say). Once you get that, it all, more or less, makes sense.