Before his time, Wales had not experienced that revolution in religious doctrine which, having its inception in Germany, had slowly made its way to England. Adams was the prophet of the movement in Wales, and his biographer, E. Keri Evans, maintains that ‘the theologian of the future will give him a prominent and, it may well be, a pre-eminent, place in the development of Welsh theology which occurred at the end of the last century.’

The two outstanding features of his early ministry were his efforts to promote temperance and his invaluable services as a catechist in the Sunday schools. In 1884 he won a prize at the National Eisteddfod at Liverpool for an essay on Hegel. From that time on he sought, in his own words, to ‘do away with the idea of contingency in theology and to substitute for it inevitability.’

In 1888 he moved to Bethesda, Caerns. His sermons now tended to stress the ethical rather than the controversial aspects of Christianity. He achieved success in the spheres of poetry, philosophy, and theology. In 1893 he shared the prize for an essay on ‘Evolution in its relation to the Fall, the Incarnation, and the Resurrection.’ He held that the Incarnation — the central fact in the history of mankind — could not be regarded as dependent on the ‘accident’ of man's fall, that a divine motive, logical and inevitable, informed the spiritual and material universe and permeated all history, and finally that evolution was nothing more than the means whereby this infinite Cause realized its objective historically. This is his most striking and positive contribution to the study of divinity in Wales.

In 1895 he moved to Grove Street, Liverpool, where he published his book Paul yng Ngoleuni'r Iesu, 1897. In this book we can trace clearly the most remarkable feature of his mind and character, namely his passionate devotion to ethics. The root of his hostility to the Calvinistic views (of arbitrary divine sovereignty, imputed righteousness, vicarious atonement, and legal justification) was his fear that all these undermined morality.

In 1913 he was chairman of the Union of Welsh Independents. In his last book, Yr Eglwys a Gwareiddiad Diweddar, 1914, he moves clearly forward through the Christ of history to a living, spiritual Christ who is the continuing foundation and authority of the Church.

In 1922 he learned that the University of Wales had decided to confer on him the degree of D.D. but, before this could be done, he was taken ill and d. 10 July 1923. He was buried at Tal-y-bont.