As the racially charged turmoil boiled over in Charlottesville, Virginia, over the weekend, President Obama responded with a series of tweets. His quote from Nelson Mandela, delivered over three tweets, became the most retweeted message in the history of Twitter. As of this publishing, the count is approaching 4 million. Viral, defined.

During turbulent times, ex-presidents straddle a perilous tightrope. Not wanting to seem too intrusive to a successor, restraint usually wins. Only extraordinary events like 9/11 or the death of a former president tend to elicit a response.

However, as the first African American president, Obama perhaps carries a unique responsibility and burden to weigh in on the current state of racial affairs. Especially as a city in the old South descends into what could only be described as riotous conditions.

Proclaimed white supremacists protesting the removal of a confederate themed statue. Modern day Civil Rights activists. The police. The National Guard. Marches. Batons. Tear gas.

Could there have been a more volatile set of circumstances for an ex-president to wade into?

Obama chose to quote this passage from Nelson Mandela's lauded autobiography, Long Walk to Freedom.

"No one is born hating another person because of the color of his skin or his background or his religion. People must learn to hate, and if they can learn to hate, they can be taught to love. For love comes more naturally to the human heart than its opposite."

It's a remarkable quote for a remarkable time.

It took Nelson Mandela nearly 20 years to complete his autobiography. His early work commenced in 1974, during his imprisonment at the infamous Robben Island prison off the western coast of South Africa, directly north of Cape Town. Mandela and his two cellmates worked together to conceal the manuscript from their captors.

At least once during his captivity, the manuscript was discovered by authorities. Again with the help of his "comrades," cellmates Mac Maharaj and Isu Chiba, enough of the text survived in draft form or in their heads to recreate the narrative.

The sweeping story begins at Mandela's birth in the Transkei territory of southeastern South Africa in 1918. It then moves to Johannesburg, where Mandela was one of the few black lawyers and the eventual leader of the African National Congress.

After his 1964 conviction for sabotage, Mandela was sent to Robben Island before being transferred to a series of mainland prisons prior to gaining his freedom in 1990, after 27 years. The finishing chapters of the book chronicle his final rise to the South African presidency in 1994, a stunning triumph for a leader and a country newly free from apartheid.

It's in the notorious Robben Island prison where Mandela became known for his leadership qualities among the prisoners and guards. He established a university-quality education program, covering such classics as War and Peace and Shakespeare. Like Viktor Frankl and Anne Frank before him, he also reached to find traces of freedom and decency in horrific circumstances. He won over many of the once-callous Afrikaner guards, foreshadowing his ability to look beyond entrenched racial camps and see into the hearts of men.

It was within the walls of Robben Island, or perhaps looking back at those times, that Mandela crafted this now resurrected quote. Here is the section in its entirety, unencumbered by a 140-character limit.

"I always knew that deep down in every human, there is mercy and generosity. No one is born hating another person because of the color of his skin or his background or his religion. People must learn to hate, and if they can learn to hate, they can be taught to love. For love comes more naturally to the human heart than its opposite. Even in the grimmest times in prison when my comrades and I were pushed to our limits, I would see a glimmer of humanity in one of the guards, perhaps just for a second, but it was enough to reassure me and keep me moving. Man's goodness is a flame that can be hidden but never extinguished."

This was written by a man in prison during one of the darker racial episodes mankind has witnessed. Yet he's able to find enough of a glimmer of humanity in his captors to go forth.

Great leaders see beyond the skin-thin surface of circumstance and into the hearts of men.

And while the ugliness of Charlottesville and a still-present racial divide play out before us, there are still men like Nelson Mandela, finding glimmers of humanity in a South African prison or a rural street in Virginia.

Now more than ever, leadership matters.