REINHOLD NIEBUHR, who died 50 years ago, on 1 June 1971, excelled in two callings: he was widely regarded as the most influential American theologian of the 20th century, and as the greatest living political philosopher of his generation.

With his gift for irony, and his awareness of the vagaries of history, he would not be surprised to learn that today — despite his acclaimed books, articles, and sermons, which elevated political and religious discourse, and challenged the powerful — he is known chiefly for one sentence, which appears on page 705 of his Major Works in Religion and Politics, in the Library of America: “God, give us grace to accept with serenity the things that cannot be changed, courage to change the things that should be changed, and the wisdom to distinguish the one from the other.”

With slight variations, that sentence is known as the Serenity Prayer. Ubiquitous on posters, plaques, cards, fridge magnets, and placemats, it has also been adopted as an official meditation by Alcoholics Anonymous. Superficially, it reads like a plea to the Most High in time of personal need or trouble. But to know only a little about its author is to realise that it is best understood as a summons to the moral clarity that makes possible a good and peaceable society, ordered by a just politics. This endeavour constituted the abiding passion of Neibuhr’s life and very public ministry.

BORN in Missouri in 1892, the son of a German Evangelical pastor, Niebuhr was one of three siblings, all of whom distinguished themselves in the study, teaching, and practice of theology and social ethics. After college, seminary, and Yale Divinity School, Niebuhr was ordained pastor in 1915 to serve at Bethel Evangelical Church in Detroit, Michigan.

In a city defined by the motor industry, industrial strife, racial and religious tensions, and the malign influence of white supremacists and the Ku Klux Klan, Niebuhr sided with the unions, spoke out against the KKK — “one of the worst specific social phenomena which the religious pride of a people has ever developed” — and, over 13 years, increased his congregation from 66 to nearly 700.

His influence and reputation grew. In 1928, impressed by the power of his preaching and writing, Union Theological Seminary (UTS), New York, appointed him Professor of Practical Theology. It was a propitious move: to a setting that fed his capacity for hard thought and prayer, and the place where he fell in love with and married Ursula Keppel-Compton, a graduate student from Oxford.

For more than 30 years, until his retirement from UTS in 1960, Niebuhr exercised a ministry that inspired students and clergy, and wrote the texts that changed many lives beyond the seminary. Moral Man and Immoral Society (1932) made a deep impression on leading British politicians, including Denis Healey and Tony Benn. The Irony of American History (1953) was described by one reviewer as “the most important book ever written on US foreign policy”. In a nation rife with racial inequality, Dr Martin Luther King, Jnr, drew on Niebuhr’s social and ethical ideals, and invited him to join the third Selma to Alabama march in 1965. A serious stroke prevented his attendance.

IN THE pulpit, Niebuhr frequently spoke without notes, engaging his listeners with his deep voice and the outstretched hand and pointed finger of the biblical prophet. He attached the deepest significance to the Bible. From its pages, he derived his understanding of human nature in all its ambiguity. In The Children of Light and the Children of Darkness (1944), he wrote memorably: “Man’s capacity for justice makes democracy possible; man’s inclination to injustice makes democracy necessary.”

Within the moral compass of scripture, and drawing on the thought of St Augustine (especially his City of God), Calvin, and Karl Barth, Niebuhr formulated the principles and insights that refused easy answers from any quarter, religious or political, and called into question the moral obtuseness that he identified within their domains. He challenged the crass optimism of liberals, and their naïve thinking concerning the perfectibility of human beings and the assured inevitability of the nation’s progress to a better future.

He also took issue with conservatives who insisted on a literal interpretation of the Bible and promulgated what, in his view, amounted to an anaemic and attenuated version of “true religion”.

With regard to America’s cherished identity as “a city set upon a hill” and blessed with a special providence, he rejected the myth of “national innocence” in matters of international relations. There could be no such thing, he argued, on the part of a nation that had “killed red men, enslaved black men, and imported yellow men” to further its ambitions and prosperity.

CENTRAL to Niebuhr’s thought was his “Christian realism”, which emphasised the sin of destructive pride that led to self-delusion in individuals and institutions — especially those making claims to perfection. He interpreted the religious life as one of perennial paradox: on the one hand, working unceasingly to transform society with faith in its graced but “indeterminate possibilities”, and, on the other, resisting the illusion that society could ever be perfected.

Now, as then, Niebuhr’s approach to matters of faith and morality offers no straightforward guide to action. The world is complex, “the mixture of good and bad in all human virtue” even more so. In such an unsettling dispensation, the Christian is required to act and choose, to embrace the path that — as Niebuhr noted towards the end of his own fruitful and demanding journey — was “full of grace and grief”.

Reading his work today, in the light of our own alarms and fantasies, suggests that we need his wisdom and unflinching self-scrutiny as much as ever.

Canon Rod Garner is an Anglican priest, writer, and theologian.