The blisters.

Any talk of Giants reliever Jeremy Affeldt’s time with the Royals has to start with the persistent blisters that plagued him. He eventually had surgery to remove the nail on the middle finger of his left hand.

“I’m not tired of talking about the finger, because I know I have to,” Affeldt once said. “I’m just tired of the finger.”

The chronic blisters twice sent him to the disabled list early in his major-leaguer career after he was the Royals’ third-round pick in 1997. That, coupled with manager Tony Pena’s inability to decide whether the 6-foot-4 Affeldt was a reliever or starter, hurt his chance for success with the Royals.

After five seasons and a 5.27 ERA, Affeldt was traded to Colorado in the summer of 2006. He helped the Rockies to the 2007 World Series, played one middling season in Cincinnati, then signed in 2009 with San Francisco, where he has come into his own.

Things are so going so well that Affeldt closed out game one of the World Series for the Giants, who are up 2-0 on the Tigers heading into Saturday’s third game in Detroit.

In four seasons with the Giants, he has a 3.19 ERA and his WHIP has gone down every year. His 261 games in relief are the 12th most in the National League since 2009.

But more than finding baseball success in San Francisco, Affeldt also discovered his voice as an advocate for social justice. He writes a lively blog at jeremyaffeldt.wordpress.com, and his Twitter account has more than 32,000 followers.

Affeldt, a Christian, doesn’t usually opine about games, but baseball is often a filter for bigger topics such as: “The World Series 2012: Who Is God’s Favorite Team?”

Other entries have included “The Transformers and the Holy Spirit,” “Argue With Me!” and “What Do You Do When You Just Want To Punch The Guy?”

Affeldt is not afraid to stir the pot.

“We’ve got the wrong idea of prosperity,” he wrote. “Prosperity is not financial. Prosperity is life. Prosperity is wholeness. Prosperity is joy.”

His passion is helping the poor, and he laments that more Americans don’t stop and realize just how fortunate they are to live in the United States.

In 2005, Affeldt, 33, and his wife, Larisa, founded Generation Alive in Spokane, Wash., where they live. The foundation’s goal is educating kids about the less fortunate and how they can help.

“I try to bring reality and bring understanding to the generation that’s next … of what poverty is in the world and what it’s doing to people,” Affeldt said on the K-Love radio network.

“We try to create an environment where kids can act and help through active compassion.”

A sample project at Generation Alive had the kids raising money for food that they then purchased and packaged for thousands of families locally in Washington state and Africa.

Affeldt is helping build an orphanage in Uganda, and the background photo of his Twitter page is a boy drinking from a well that Affeldt helped fund in Africa.

“What he talks to (kids) about is compassion and sympathy,” said Darrin Duty, the executive director of Generation Alive. “Instead of just seeing someone’s pain and feeling bad, compassion actually acts upon it. That really sums up what he wants to see happen.

“Jeremy is a man of very deep faith, and I really believe his faith has moved him more than it probably moves most. He believes in putting action to your words. That defines who he is, and he has a huge heart for youth.”

That’s why Affeldt began working with the San Francisco-based Not For Sale, an organization that fights human trafficking and modern-day slavery.

He had been unaware that it was even a problem before joining the Giants.

“I really didn’t understand it four years ago,” Affeldt said. “I was in the same boat a lot of people are, thinking, didn’t slavery cease to exist in the 1800s? When I started reading about all these areas of poverty where human trafficking was at its highest point, it started to really wear on me.”

What digs at him most is the thought of kids and teens being sold into slavery. They will never have a chance to live out their dreams.

Affeldt has pledged $250 for every strikeout, save and hold he collects in a season for Not For Sale, and he has donated more than $30,000 in his career. He’s also been a spokesman publicly (he’s the organization’s ambassador with Sarah Ferguson, the Duchess of York) and behind the scenes, where he recruited the Cardinals’ Matt Holliday to donate to the cause.

According to the organization’s website, there are 17 players helping Not For Sale, including teammate Brandon Belt.

“Athletes are great mentors for the issue of human trafficking,” Affeldt wrote. “We’ve been able to accomplish our dreams, but that started with being allowed to dream in the first place. Slavery kills the ability to dream.

“It’s so important for former child slaves to be free to play. It’s through play that they can start dreaming again.”