If the goal is to map the evolving landscape of American religion, the late George Gallup, Jr., once told me, it is crucial to keep asking two kinds of questions.

The first kind attempted to document things that never seemed to change or that were changing very, very slowly. Thus, Gallup urged his team to keep using old questions his father and others in the family business began asking in the 1940s and '50s, such as how often people attended worship services, how often they prayed and whether they believed in God.

The second kind of question, he said, tested whether these alleged beliefs and practices affected daily life.

"We revere the Bible, but don't read it," he warned, in one 1990 address. "We believe the Ten Commandments to be valid rules for living, although we can't name them.

"We believe in God, but this God is a totally affirming one, not a demanding one. He does not command our total allegiance. We have other gods before him."

About that time, I shared a set of three questions with Gallup that I had begun asking, after our previous discussions. The key, he affirmed, was that these were doctrinal, not political, questions. My journalistic goal was to probe doctrinal changes that revealed fault lines in churches. The questions:

* Are biblical accounts of the resurrection of Jesus accurate? Did this happen?

* Is salvation found through Jesus, alone? Was Jesus being literal when he said, "I am the Way, the Truth and the Life. No one comes to the Father except through me."

* Is sex outside of marriage a sin?

Through the years, I have discussed these questions -- my GetReligion.org colleagues call them the "tmatt trio" -- with journalists and other pollsters, seeking their insights. However, the leaders of LifeWay Research recently went so far as to write my questions into a new "Theological Awareness Benchmark Study" conducted for Ligonier Ministries.

The results echoed decades of work by Gallup and others indicating that surprisingly high numbers of Americans affirm -- in words -- many traditional religious beliefs. Yet when questions push them toward real conflicts with life in mainstream culture, an increasing number of Americans waffle and move toward what LifeWay President Ed Stetzer calls the "mushy middle."

On one side -- approximately 25 percent of those polled -- are "convictional" believers who actively practice their faith, he said. On the other side are truly secular, vaguely spiritual or "religiously unaffiliated" Americans, the growing "nones" camp that received so much media attention after a 2012 study released by the Pew Forum on Religion and Public Life. And in the middle?

To no one's surprise, the resurrection question drew the most positive responses -- with 45 percent of those polled strongly affirming that doctrine and 23 percent agreeing "somewhat." At the denominational level, 91 percent of evangelical Protestants affirmed the resurrection, to one degree or another, along with 84 percent of black Protestants, 73 percent of "mainline" Protestants and 73 percent of Catholics.

Concerning belief that salvation is through Jesus alone, 35 percent strongly agreed and 18 percent agreed "somewhat." However, there were clear denominational fault lines -- with 85 percent of evangelicals and 74 percent of African-American Protestants agreeing. However, only 55 percent of "mainliners" and 45 percent of Catholics affirmed this doctrine.

Similar cracks appeared on my third question, with 31 percent strongly agreeing, and 17 percent "somewhat," that sex outside of marriage is sin. However, 26 percent of those polled strongly disagreed and 17 percent disagreed "somewhat." In the pews, 76 percent of evangelicals and 74 percent of black Protestants endorsed this belief, as opposed to 44 percent of mainline Protestants and a mere 40 percent of Catholics.

In Gallup terms, the resurrection question probed an orthodox doctrine that many of those polled would find hard to reject. The questions about salvation and sex, however, pushed many people into conflict with life in modern America.

"America is a churched nation, for the most part. Most Americans are either going to church or they used to go to church," Gallup told me in 2004. "At some point we need to start focusing more attention on what is happening or not happening in those churches. ... Are our people learning the basics? Is their faith making a difference in their lives?"

    NEXT WEEK: Probing faith questions in "mushy middle."