I am a Chinese scholar. It is said that Thomas Aquinas gave up his research on rational theology before his death and confessed his research is nonsense and it means he retrogressed to Tertullian standpoint (embracing credo quia absurdum). Is this true?
Good question. The view of Thomas Aquinas which you mention is quite common, but profoundly misleading.
At several points in his life, St. Thomas is said to have experienced divine visions. In one of them, Christ appeared to him and said, “You have written well of me, Thomas. What would you ask of me?” St. Thomas replied, “Only you, Lord.”
Later, at the end of his life, he is said to have experienced another vision. Afterward, he told one of his brothers in the Dominican order that he could no longer continue to write, because in comparison with what had been revealed to him, all that he had written seemed like straw. This is the statement which gives rise to the misunderstanding about which you ask.
But it is very important to remember that St. Thomas never repudiated what he had written before. Though his past writing seemed to him “like” straw in comparison with the vision, it was very good so far as it could go. Straw itself is good. The Bread of Heaven is better.
This should not surprise us. Throughout his life, St. Thomas had always argued that what can be known about God by reasoning is excellent, but it is only about God. The vision of God in Himself, granted to the souls of the redeemed in the next life, is infinitely superior. Now that he was standing at the very door to that life, it was difficult for him to give his attention to anything less.
As St. Paul had written, in a passage which St. Thomas quoted often, “For now we see in a mirror dimly, but then face to face. Now I know in part; then I shall understand fully, even as I have been fully understood.”