Possessing outstanding academic qualifications, Daniel was one of the most able theologians of his generation, combining wide knowledge, an unfailing memory and a superb analytical mind. He was strongly influenced by the teachings of Karl Barth and Rudolph Bultmann in the stirring days of their early efforts. He shared their challenging spirit and their keen criticism of current theological thinking, creating thereby fierce opposition. However, Daniel was the most able interpreter of the reaction against the liberal theology movement in Wales . Despite this, his literary contribution to this field was sparse. He published Dysgeidiaeth yr Apostol Paul ( 1933 ) and a handful of articles in various journals. He was not ordained but there was great demand for his services as a preacher because of the stirring power of his sermons which combined a broad culture with fiery conviction.

He was a staunch nationalist . He came to early prominence as one of the leaders of Plaid Genedlaethol Cymru which was established in 1925 . He was a regular contributor to its newspaper, Y Ddraig Goch , and he stood as a candidate in four general elections . He was a vice-chairman of the party from 1931 to 1935 and he followed Saunders Lewis as its chairman in 1939 and held the office until Aug. 1943 .

Daniel was notable for his broad culture, his exceptionally brilliant mind and the strength and richness of his grasp of the Welsh language, both orally and in writing, his zeal for everything that was good in Wales and for the Christian faith above all else.