It is more correct to say that Thomas Aquinas is not impressed with his own theology. (Nor am I, as a Zen Buddhist, for other reasons.) How did this happen to one of the Doctors of the Church, known as the greatest Catholic theologian? With great difficulty (as usual), specifically by passing beyond the limits of theology.
On 6 December 1273, while Thomas was celebrating Mass, he experienced an unusually long ecstasy.[60] He then abandoned his theological writing, saying, “All that I have written seems like straw to me"[61] (mihi videtur ut palea).[62] As a result, the Summa Theologica would remain uncompleted.[63]
Murray, Paul (2013). "10. The collapse, the silence". Aquinas at Prayer: The Bible, Mysticism and Poetry. Bloomsbury. ISBN 978-1-4411-0589-9.
I have long understood this to be the most impressive fact about Aquinas—that he turned into a Zen water buffalo.