I’ve come to this view in publishing a small book of reflections on the last sayings of Jesus from the cross — a devotional exercise, to be sure, but one that’s brought to mind the motive force of a Christian message based not on Fox News but on what those first-century words meant then and can mean now. “Father, forgive them”; “Assuredly, I say to you, today you will be with me in Paradise”; “Father, into thy hands I commend my spirit” — these remarks from the Gospel accounts of the Passion form a kind of final sermon from Jesus, one about forbearance, duty, love and mercy.

I am a Christian (a very poor one, but there we are), but I am also a historian, and contemplating the beginnings of the story of my ancestral faith has led me to think about the uses of Jesus down the eons. Yes, Christianity has been an instrument of repression, but in the living memory of Americans it has also been deployed as a means of liberation and progress — which feeds the hope that it can become a force for good once more.

The secular wish to banish religion from the public square is perennial but doomed; one might as well try to eliminate economic, geographic or partisan concerns. “All men,” Homer wrote, “have need of the gods,” and the more productive task is to manage and marshal the effects of religious feeling on the broader republic. “In ages of faith the final aim of life is placed beyond life,” Alexis de Tocqueville said in “Democracy in America,” written in the Age of Jackson. “The men of these ages,” he added, “learn by insensible degrees to repress a multitude of petty, passing desires.”

Don’t take my word for it. Take, instead, that of John Lewis and of the Rev. Dr. Martin Luther King Jr., men whose Christian belief brought America to account on the question of domestic apartheid just over a half century ago. Their words and actions can be traced directly from the words and actions of Jesus. King’s vision was grounded in both the Bible and in Gandhi. “It was the Sermon on the Mount, rather than a doctrine of passive resistance, that initially inspired the Negroes of Montgomery to dignified social action,” King recalled of the Montgomery bus boycott. “It was Jesus of Nazareth that stirred the Negroes to protest with the creative weapon of love.”

King had been deeply influenced by the theologian Walter Rauschenbusch and his 1907 book “Christianity and the Social Crisis,” which argued that Jesus called the world not simply to contemplate but to act. “The Gospel at its best deals with the whole man, not only his soul but his body, not only his spiritual well-being, but his material well-being,” King wrote in a Rauschenbusch-inspired passage. “Any religion that professes to be concerned about the souls of men and is not concerned about the slums that damn them, the economic conditions that strangle them and the social conditions that cripple them is a spiritually moribund religion awaiting burial.”