But the war did have a devastating influence on American religion and its grip on the larger culture. Here is his conclusion.
From the Civil War onward, American Protestantism would be locked deeper and deeper into a state of cultural imprisonment, and in many cases, retreating to a world of private experience in which Christianity remained of little more significance to public life than stamp-collecting or bridge parties. Appeals to divine authority at the beginning of the Civil War fragmented in deadlock and contradiction, and ever since then, it has been difficult for deeply rooted religious conviction to assert a genuinely shaping influence over American public life.
In exposing the shortcomings of religious absolutism, the Civil War made it impossible for religious absolutism to address problems in American life—especially economic and racial ones—where religious absolutism would in fact have done a very large measure of good. Some leaders, Martin Luther King prominent among them, have since invoked Biblical sanction for a political movement, but that has mostly been tolerated by the larger, sympathetic environment of secular liberalism as a harmless eccentricity which can go in one ear and out the other. “Never afterward,” wrote Alfred Kazin of the war, “would Americans North and South feel that they had been living Scripture.” I do not know that Americans have been the better for it.
I probably would not have used the phrase "religious absolutism" to describe the positive impact that Christianity could have had on post-bellum American life.