Even before his skull was fractured by an Alabama state trooper during the 1965 Selma-to-Montgomery march, John Lewis had, along with Martin Luther King Jr., become the personification of nonviolence in the Civil Rights Movement.

Despite being beaten and arrested time and again at sit-ins in Nashville, Tennessee, on the Freedom Rides and elsewhere, Lewis’ ability to repeatedly endure violence and hatred with dignity is almost unfathomable.

David Greenberg’s biography, “John Lewis: A Life,” justly celebrates this part of Lewis’ life and adherence to the concept of “good trouble” — disruption to bring about positive change — but Greenberg shows how much and how well Lewis adapted to changing times in the movement and society. In the 1970s, he fought within the system to preserve the voting rights he’d risked his life for, and later he became a voice of moral authority in Congress. He spoke out as an early proponent of gay rights and other issues, fought to get the Smithsonian National Museum of African American History and Culture built, and constantly kept civil rights in the foreground.

Greenberg spoke recently by video about what we may be able to learn from Lewis, whom he refers to as this “saintly” man. This interview has been edited for length and clarity.

Q Beyond Lewis’ tremendous activism in the early 1960s, what made you want to write a biography about him?

A He was someone who had this tremendous second act. Many figures from the Civil Rights Movement did very admirable things, but he became this icon. That was partly, of course, appreciation of his heroism at Selma and the Freedom Rides and so on, but it also had to do with his role in politics, as a moral voice in Washington.

I’m not a cynic about politics. We need politicians, but good and effective politicians. I came to admire the way that John Lewis could be a success in protest and then in politics and stay the same man all the way through. He learned a new set of skills — how to work the Democratic leadership, knowing when to find a partner across the aisle, knowing when to compromise, even when to go negative in a campaign — but I don’t think he fundamentally changed his character. I find each part of him and his career to be admirable in different ways.

Q You write about his moral authority in Congress. I wonder if that would be less valued in today’s polarized climate.

A That’s a fair question. Since his death, things have gotten more polarized, more intolerant. He was a guy who had this amazing partnership with Republican Sam Brownback to get the Museum of African American History built. He took Kevin McCarthy on the Selma march with him one year and Lewis was very solicitous, making sure that McCarthy and his family appreciated learning about it and were respected.

Q You recount a time when someone called Lewis’ office, spewing all sorts of racist language. Lewis called the man back, which “stunned the constituent, who immediately apologized and began talking respectfully.” Is there a lesson there we all could learn today?

A He had qualities very few of us could muster; he showed forgiveness and love and could withstand violence in ways most of us would not be capable of doing. He was not a saint but he was saintly. Not everybody would succeed with that, but it’s something we can learn from. The extreme to which Lewis went — saying you have to feel love for George Wallace’s troopers — may be hard for people to emulate, but on a smaller scale, we can still bring that thought to politics and personal relationships.

Q Your book details Lewis enduring more violence and arrests than most people know about.

A There’s one wonderful little story in Nashville when he’s punched in the mouth, and there’s a headline about it. And he thinks, “Why is that such a big deal? I was just punched in the mouth.” It was old hat to him.

He was the most ready and willing to do all this nonviolently, but there were so many young men and women who were ready to get hit, to put their life on the line, because they believed in this cause. Not as many today are that willing or capable of that kind of courage. They get harassed by the cops and they complain; they think it’s unfair that they might have to go to jail. Lewis just said, “Of course we go to jail. That’s part of what this is all about.”

Q But you note that someone tells Lewis that while he believed nonviolence accomplished so much, the fear of violence behind it was actually what was effective. Lewis couldn’t acknowledge that. What about you?

A It’s a good question, Lewis maintained that we must stick to the path of nonviolence. Lewis believed in “I’m going to put on my best suit and tie and conduct myself as a model human being and that will be the most powerful weapon.”

And there’s a lot of scholarship arguing that nonviolent action has been far more effective at bringing about political change than violence. But I put in that exchange because I can’t say confidently that one or the other conclusion is correct. Throughout the ’60s, while Dr. King and Lewis were leading nonviolent actions, there were other episodes where things turned violent, where there was fear of rioting, which worried politicians.

So, both things were in the air, and I don’t know that we can say definitively what ultimately brings about the major legislation and Supreme Court rulings. But you do see that King’s approach has this tremendous moral force, and you see a dramatic sea change in opinion among Whites as a result of this really heroic self-restraint that people like John Lewis exercise. So I don’t think it can be reduced to simply a fear that something worse is around the corner.

Q Could nonviolence be as powerful today; would social media amplify or undermine it?

A It can be, but it’s a hard sell (in today’s society). I’ve talked to students and a lot of them are very cynical about it. They say, “Why should we be the ones to endure violence? Why should we be the ones to be well-behaved?” Which, of course, misses the point.

Q Do you hope this book helps them see the point?

A I write history to tell stories I think are important and meaningful. I don’t have great confidence that it wins people over to a point of view or an ideology, but if it leads people to discover John Lewis and the power of the nonviolent movement, that’s great.