Amy Zehnder has seen giving on a huge scale. As a senior wealth dynamics coach in Denver for U.S. Bank's Ascent Private Capital Management, she helps ultra-wealthy people ($50 million or more in assets) manage and plan their charitable giving.

But when asked for an example of how charitable giving can change a family, she mentions what she observed in her family of friends. Her friends took their teenagers on a vacation to do charitable work with a group of kids in New Mexico.

"The family spent a week helping and serving the kids," Zehnder says. "It bonded the family together. It created unity. It created purpose. And it changed how they are behaving on a daily basis."

And that, she says, is what she tries to do for her company's wealthy clients and their families, learn "the spirit of giving and how powerful it is."

And that spirit of giving is big in the United States. According to CharityNavigator.org, Americans gave $316.23 billion in 2012 (about 2 percent of GDP). Of that, the majority (72 percent) came from individuals; corporations account for 6 percent of charitable donations.

And the largest benefactors of this giving are religious organizations — receiving 32 percent of all donations. Much of these donations go to local houses of worship, according to CharityNavigator.org.

With all this giving going to religious groups, it may appear that religious people are more charitable than non-religious people. But are they? When experts familiar with charitable giving look at the reasons for giving, they find a complex mix of motivations — some that fit tightly into religious life, and others that are less so.

Reasons to give

Jason Franklin divides the motivations for giving into six different areas.

One of those areas is faith. Franklin, adjunct professor of philanthropy at NYU and executive director of Bolder Giving (a nonprofit group that spotlights everyday philanthropists), says many people say they give because of their faith or religious teaching. "Every major religion has teachings on giving," he says.

And so people give to their churches or to people in need.

Another reason for giving is enthusiasm for a cause. "Giving is only a vehicle to express their passion," Franklin says.

He also says it is common for people to give to many different organizations that express different passions they have from helping homeless children to working for climate change.

The third reason people give is the desire to make an impact on the world. This is particularly appealing to people who have larger amounts of wealth.

A fourth reason is fairness; people see inequity in the world and they want to do something to help ease the results of that inequity.

The fifth reason people give, Franklin says, is simplicity. People become concerned about consumerism and their own consumption and begin to cut back — giving the excess to various charities. "The act of giving changes your perspective on life," he says. "They want that shift in perspective."

The final reason people give is one that Franklin says is often overlooked: Joy. People like how it makes them feel. Franklin says what one giver said sums it up: "The best money I ever spent I gave away."

Giving votes

Cliff Guthrie says charity is like voting.

"Whenever people give to a charity," says Guthrie, an associate professor who teaches about philosophy, religion and ethics at Husson University in Bangor, Maine, "every dollar we spend, no matter what it is on, is a vote for the way you want the world to be. Every dollar you spend is a vote."

He says research shows people give to things they care about. "We tend to give to our groups," he says.

So religious people will give to the religious causes they care about.

Guthrie started giving money to the Metropolitan Opera after he started going to their performances. "I loved them so much I wanted to support them," he says.

The "voting" also works the other way. People will give money to organizations that are fighting against things they do not like — such as donating to Democratic causes if a person did not like George W. Bush or donating to politicians promising to defeat Obamacare.

Religious giving

Franklin says there is a debate about whether, when people give to religious organizations, if they are really giving to the community. "People who are actively giving to their church see the good works it does in the world," he says. "The critics, those not in that church, may say the church does not help in the broader community. Motivation is in the eye of the beholder."

A study by the Chronicle of Philanthropy last year looked at giving patterns across the U.S. It found that religion has a "big influence on giving patterns" and that "regions of the country that are deeply religious are more generous than those that are not."

But if that religious giving is taken out of the mix and only secular gifts are counted, suddenly New York jumps from No. 18 on the list of charitable giving to No. 2 and Pennsylvania, which was No. 40, becomes the fourth most charitable state.

Guthrie says religious belief is so diverse it is difficult to make easy conclusions. He also says non-religious people are also diverse and probably, like religious people, their "giving follows where they spend their time."

And where people spend their time is a key to becoming more charitable, Guthrie says.

How to be charitable

Zehnder's friend's children were changed by experiencing face-to-face the needs of others. The children came up with the idea on their own to save money for that New Mexico charity by foregoing other previously normal activities such as going out to restaurants.

"At the end of the year, the parents could probably give twice or three times more than they are raising this way," Zehnder says. "But that is not what this is about. The kids are now onboard with what it means to give."

Zehnder also notices how, in her wealthy clients, working on charitable causes can bring families together.

Guthrie says if people want to expand their heart and be more charitable, they need to go to people in need and just be with them. "They need to see them as human beings and not as statistics that are far away," he says. "People's money follows their behavior, not the other way around."

Zehnder visited Africa and saw the impact her own contributions could have on families there. "I had a whole new perspective on wealth after coming back from Africa," she says. "If you know what carpet is, then you are a wealthy person compared to them. If you have carpet, you have enough to give to these people who have nothing."

Social pressure

Guthrie says social pressure also is a good motivator. "If you hang around people who have a habit of giving, that will rub off on you," he says. It is in this type of motivation to give, the actual contact with other people in need, that churches may have a leg up on the secular world. "Just being a part of a group that reminds you of the needs of other people," he says, "is why we see overall giving higher where there is church involvement."

Guthrie knows about the support churches can give to members. He was at one time a United Methodist pastor, but now says he is "completely out of religion, except as a scholar."

"That is the one thing I really miss from when I was involved with church," he says, "was there was always someone there to help out. … I have that with our neighbors, but it is not as regular and as consistent."

For Franklin, the NYU adjunct professor of philanthropy, giving, whether religious or non-religious, is at its core about being good people.

"Every major world religion and every well-respected humanist philosophy all teach about being concerned about more than just yourself," he says. "Giving is just another way we carry out those goals."