What an exceptional mind this Saint had! He once gave thanks to God that he had never read a page he did not understand.
The following is excerpted from a biography of St. Thomas I found on the EWTN website:
It is not surprising to read in the biographies of St. Thomas that he was frequently abstracted and in ecstasy. Towards the end of his life the ecstasies became more frequent. On one occasion, at Naples in 1273, after he had completed his treatise on the Eucharist, three of the brethren saw him lifted in ecstasy, and they heard a voice proceeding from the crucifix on the altar, saying "Thou hast written well of me, Thomas; what reward wilt thou have?". Thomas replied, "None other than Thyself, Lord" (Prummer, op. cit., p. 38). Similar declarations are said to have been made at Orvieto and at Paris. On 6 December, 1273, he laid aside his pen and would write no more. That day he experienced an unusually long ecstasy during Mass; what was revealed to him we can only surmise from his reply to Father Reginald, who urged him to continue his writings: "I can do no more. Such secrets have been revealed to me that all I have written now appears to be of little value"
In this we see what we have seen again and again in the lives of the Saints: that even a deep understanding of the Church's teachings and a clear intellect united to a perfect faith are nothing compared to a real encounter with God.
You can read the rest of the biographical sketch here.