It was the kind of cryptic theological statement that is often found stuck on automobile bumpers.

This sticker said: "Don't let my car fool you. My treasure is in heaven." This echoed the Bible passage in which Jesus urged believers to, "lay up for yourselves treasures in heaven. ... For where your treasure is, there will your heart be also."

This sticker's creator probably intended it to be displayed on the battered bumper of a maintenance-challenged car, noted sociologist Christian Smith, director of the Center for the Study of Religion and Society at the University of Notre Dame. Thus, the sticker suggests that the driver knows his car is a wreck, but that he has "other commitments and priorities" that matter more.

But Smith was puzzled when he saw this sticker on a $42,000 SUV parked at a bank.

"Let's be clear. I have no problem with abundance. I have no problem with capitalism," he said, speaking at Gordon College, his alma mater near Boston. "The person driving this car may give away 40 percent of their income. I have no idea. I'm not trying to nail people who drive SUVs or whatever.

"But it seems to me that the meaning of this bumper sticker has changed from what I thought was the original meaning to, 'Well, Jesus didn't quite get it right, because I have a lot here and I also have it in heaven, too. So I have all the bases covered.' "

After years of digging in the data, Smith has reached some sobering conclusions about believers and their checkbooks.

It's true that Americans give away lots of money, in comparison with people in other modern societies. It's also true that religious Americans are much more generous than non-religious Americans. But here's the bottom line: The top 10 percent of America's givers are very generous, while 80 percent or more rarely, if ever, make charitable donations of any kind.

"This is the glass half-full perspective," said Smith. "We're not doing too bad. We're doing pretty good. However, most American Christians turn out to be stingy financial givers -- most, but not all."

Stingy? Smith believes that the vast majority of affluent American Christians will see they are guilty as charged, if they candidly contrast the amount of money they give away with the doctrines that are proclaimed in the pulpits of all traditional churches.

The result is a laugh-to-keep-from-crying paradox. In fact, Smith considered using another title for his chapel address: "Why does $30 seem like so much to give in church and so little to spend in the restaurant after church?"

The stakes are high in this spiritual struggle. Recent research indicates the combined incomes of active U.S. Christians -- people who frequently go to church -- reached about two trillion dollars in 2005.

The Bible's minimum standard for giving is the "tithe," Smith noted, and it asks believers to give away at least 10 percent of their income. Do the math: 10 percent of two trillion dollars is a lot of money.

"When you study American religion," said Smith, "it quickly becomes clear how important having material resources is if you want to get anything accomplished. ... There are all kinds of things that church leaders say that they are supposed to be doing, yet they struggle to do them because they do not have the resources to act."

Ministers are often afraid to talk about this issue openly, in large part because they "feel like they're in a compromised position," he noted. "They don't want people to think that they are standing up there in the pulpit trying to raise their own salaries."

Truth is, people in the pews would probably prefer to hear a clear, unapologetic message about stewardship from someone who is not ordained. But Smith stressed that anyone who talks about faith and money has to be able to "communicate a spiritual vision that is larger than trying to pay the light bill at the end of the month."

When it comes to tithes and offerings, parents are even more important than pastors.

"People who give generously," said Smith, "almost always say, 'This is just the way my parents raised me. This is part of who I am and what I believe. My parents taught me to be thankful and to help others.' "