WHEN I WAS FIRST elected as a state senator in 2000, there were a number of formidable political figures from Philadelphia who explained the inner workings of the state government to me. And they were helpful to a young guy from Northeast Philly just getting his start in Harrisburg.

But there was one quiet woman who gave me a perspective on public service that was different from all the others and who taught me some of the most valuable lessons I've ever learned about what it takes to make a positive difference in people's lives.

State Sen. Shirley Kitchen really cared about everyday men and women, especially those who lacked influence in the halls of power. Standing up for the little guy wasn't just something she did every now and then. It was her purpose.

Kitchen has retired after 20 years in the state Senate - her last official day was Wednesday - and she will be missed more than most people in Pennsylvania will ever know. She championed the most vulnerable people in the poorest of neighborhoods. She tried to be a voice for people who had no one else to speak for them, to be an advocate for communities that had no one else fighting for them.

She was not someone of politics or party who reached out to the grass roots. Rather, she was someone of the pure Philadelphia grass roots who went to politics and government to serve the people.

She used to joke that the difference between politicians from Philadelphia and other places is that when the news media come around, other politicians run away, and we run to them. But that wasn't Shirley so much.

Kitchen did not give a lot of speeches. She didn't attract a lot of attention to herself. She was soft-spoken, but behind the scenes, she was a steady guide, especially for those of us from Philadelphia. And when she did talk, we all listened.

She was like a stern mother at times. She was streetwise, not afraid to give you love, but not afraid to give you straight talk when she thought you needed to hear it.

Shirley and I sat next to each other in the Senate Democratic caucus room when I became a state senator, and I used to bounce questions and ideas off her during meetings. She was from North Philadelphia, and I was from the Northeast, so we had different constituencies. Or so I thought.

But the more we talked about things, the more I realized that those differences were superficial rather than fundamental. In reality, it was the same constituency. Shirley helped me realize that all communities have their problems, and that no community exists in isolation. The problems of one community are never confined there. The problems of one person who faces injustice are never just problems for that person. They hinder us all in one way or another and diminish our humanity.

She helped me to understand that sometimes people cope with difficult circumstances the best they know how, and when they do, they mess up on occasion. When that happens, we shouldn't give up on them, but instead give them a hand up.

She believed in the power of education and in the power of rehabilitation. She was ahead of her time in seeing the need to improve the criminal justice system, before that notion became trendy. She understood that we shouldn't be wasting resources to merely warehouse people in prison, but instead should be trying to lead them onto a better path.

That's a philosophy I've taken deeply to heart in my constitutional role as lieutenant governor to chair the Board of Pardons. We are trying to turn it into a state agency that reaches out to give ex-offenders a second chance when they have truly earned it.

I've had many mentors in my life, and Shirley Kitchen was one of the special ones. She showed me much, especially how to walk the road of social justice. I'll forever be grateful to her.

Mike Stack is lieutenant governor of Pennsylvania and served for 14 years with Shirley Kitchen in the state Senate.