The work of Thomas Aquinas is a whole continent. Where to begin? I have found the books of the late Herbert McCabe helpful, and must now add (above) Denys Turner’s recent book Thomas Aquinas: A Portrait to the pile. First, as Turner points out, Thomas is not afraid to ask questions. This probably goes against the grain of caricatures of medieval theologians as toeing the line theologically. Turner suggests Thomas is “braver” than even more recent questioners, who often tailor the question to the sort of response that is considered legitimate.
Thomas is also full of common sense. Against the modern Cartesian picture of the mind and body (or mind and soul) as separate entities, Thomas knows that any thinking about the non-material is grounded in the material. For Thomas, a soul without a body is not a person. Lest this seem heretical, remember that Christians believe in resurrection of the body, not migration of the soul. And even for non-Christians, Thomas takes the sensible line that our thinking must be done via flesh and blood. Our minds are not simply our real selves trapped in a body.
Thomas also reaches for the stars when thinking about God. He forever reminds us that our concepts of God are usually limited in some way, and are therefore not of God. For example, he says, famously, when we think of God’s relationship to the universe, it is not “the universe + 1”. God is not just another “thing” that sits outside the universe, somehow separable from the universe, like the driver of a car. This is not merely an academic exercise, it is important for how Christians defend their perhaps irrational seeming faith, and for atheists who think they have argued away God, rather than simply “a god”.