BOTH “Christian” (religiously) and “Left” (politically) are contested concepts; putting the two together sharpens rather than resolves the debates over their meaning. Clear and simple definitions are almost certain to be wrong; undoubtedly the only sensible strategy is to undertake the fullest possible engagement with the range of writers and ideas that can reasonably claim to be part of the “Christian Left”, and to hope that some of the family resemblances will emerge and, with them, an increased clarity about their range and coherence.

That is the strategy pursued with enormous energy by Anthony Williams. Anyone seeking a compendium of the diverse manifestations of Christian engagement from the Left will find in his book a valuable resource and, in the range and organisation of the material, an achievement, often breathtaking if, at times, inevitably breathless, as he moves from one thinker to another.

There will be very few readers, however familiar with the field, who will not be introduced for the first time to some significant and neglected contributors to the development of Christian radicalism, along with those who will immediately come to mind when “Christian Socialism” is mentioned: F. D. Maurice, Stewart Headlam, William Temple, Dorothy Day, Gustavo Guttiérez, and contemporary political theorists such as John Milbank and Adrian Pabst.

With its 30 pages of footnotes and upwards of 900 citations (a bibliography would have been helpful), it would be easy to rank this as a book only for scholars. It is also, however, readable, passionate, and accessible.

The international scope of the book is particularly helpful. Beginning with the 19th-century foundations of British Christian socialism (though how precisely “socialist” were the founders of the Guild of St Matthew is something that Williams quite properly questions), there is then a chapter on the challenges that have faced “the Left” since the Second World War. Religious socialism in mainland Europe shows up great differences of context and theology, compared with the British scene.

The “social gospel” is part of the very different history of the Left in the United States, followed more recently by the civil-rights movement, Black Power, and the “red letter” Evangelicals, inhabiting an environment deeply hostile to all things “socialist” and “Left” and with a highly dominant “religious Right”. There are two chapters on liberation theology, first in Latin America (majoring on the thinking of Gutiérrez) and then a chapter on manifestations of liberation theology elsewhere — in Asia, Africa, and the Middle East — with a more extended section on feminist liberation theology.

It is at this point that the issue of the boundaries of the author’s theme become blurred. That is not Williams’s fault, for the “Left” is a title now claimed by all sorts of movements and individuals often far removed from the collectivist commitment that, surely, is the central political and economic thrust of socialist, “Left”, thinking.

In this respect, some of the omissions are striking: there is no mention of the Christendom movement, of Maurice Reckitt and V. A. Demant, people for whom “socialist” would have named what was their pre-eminent political and economic agenda; and although Paul Tillich’s thinking is described, there is no mention of his very direct exposition of socialism in his early The Socialist Decision.

The question is, for all the comprehensiveness of the material surveyed, how far the resulting essay clarifies the contested areas that it examines. It is bookended, at the start, by Donald Trump’s extraordinary appearance with a Bible outside St John’s Episcopal Church, Washington, and, at the end, the author’s consideration of “Where next for the Christian Left?”. Between these two, it is perhaps possible to discern Williams’s agenda more clearly.

As a prelude to his conclusion about the future of the Christian Left, Williams mounts a critique of interpretations of the parable of the sheep and the goats which suggest that the parable is about being good to those in need. Williams supports the view that those to be helped are not all those in need, but the “brothers and sisters of Christ”: that is to say, believers. But Jürgen Moltmann (a striking omission from a book on Christian radicalism) has cogently argued that the brothers and sisters are all in need: they are, because of that, the Christ whom believers are called to serve.

Williams is of the view that the Christian Left’s current liberal stance towards orthodox faith makes it vulnerable to being co-opted into the identitarian politics of the secular Left, focusing on sexuality and gender politics, for example. It is the conservative faith of the “brothers and sisters” that stands the best chance of “demonstrating that Christianity need not belong to the conservative Right and making the ethical case for an economic system subject to fairness and the common good”.

The resources that Williams deploys make the book really worth while; to have allowed himself a bit more space to develop that critical point of debate would have made it even more so.

The Rt Revd Dr Peter Selby is a former Bishop of Worcester, Bishop to HM Prisons and President of the National Council for Independent Monitoring Boards.

The Christian Left: An introduction to radical and socialist Christian thought
Anthony A. J. Williams
Polity Press £17.99
(978-1-5095-4282-6)