His friendship with the Austrian Catholic theologian Baron von Hügel led him to closer study of spirituality, resulting in a book, The Idea of Perfection in Christian Theology (1934), which remained in print for many years.
The result of these problems is an 'intramundane asceticism', whereby the one assured of sanctification merely endures secular life, allowing a barrier to exist between one's work and worship.
"[8] In 1927 Flew was appointed Greenhalgh professor of New Testament language and literature at Wesley House, Cambridge, a theological college founded in 1921, of which he was principal from 1937 to 1955.
He became a keen contributor to the Cambridge New Testament Seminar, held under the chairmanship up to 1935 of Francis Crawford Burkitt, leaving an account of it in an obituary for Burkett in the Proceedings of the British Academy.
On the academic side, one recent scholar concluded, "The Idea of Perfection in Christian Theology (1934) was a meticulous piece of scholarship on a theme dear to Methodist hearts, though it was as an ecclesiologist that Flew would exert widest influence on Protestant thought.
"[11] Particularly relevant at the time was the incisive contribution it made to the then current debate on episcopacy, by showing "the early [Christian] communities to have been independent and unstructured.
Having attended several pre-war preparatory conferences, he was appointed vice-chairman of the provisional committee of the World Council of Churches after the war and took a leading part in its inaugural meeting in Amsterdam in 1948.