To close out his speech accepting the Democratic nomination for president on Thursday, Joe Biden turned to a passage he knows well.

“The Irish poet Seamus Heaney once wrote: ‘History says / Don’t hope on this side of the grave / But then, once in a lifetime / The longed-for tidal wave / Of justice can rise up / And hope and history rhyme.'”

Then, the former vice president added, “This is our moment to make hope and history rhyme.”

If Biden’s well-received address at the DNC was the biggest of his five decades in politics, then it was only fitting that he bring a favorite poet – and favorite poem – along with him.

Throughout his career, rising from a county councilman in Delaware to the highest rung of the Democratic Party, he has gained a well-deserved reputation for peppering speeches with lines from Heaney and fellow Irish poet William Butler Yeats.

Democratic presidential candidate former Vice President Joe Biden speaks during the fourth day of the Democratic National Convention, Thursday, Aug. 20, 2020, at the Chase Center in Wilmington, Del. AP Photo/Andrew Harnik

As a teenager, he would recite Yeats’ verses in his bedroom while working on his stutter. When he reached the Senate, it appeared that penchant for the verses from the homeland of his ancestors had been hard to kick.

“My colleagues always kid me about quoting Irish poets all the time. They think I do it because I’m Irish,” he once told officials in Beijing. “I do it because they’re the best poets.”

Of all his poetic recitations, though, Heaney’s line on “hope and history rhyming” has had particular relevance for him and many other politicians over the years.

Heaney adapted “The Cure at Troy” from the Sophocles play, “Philoctetes,” which concerns the closing days of the Trojan War. Under Heaney’s 1991 verse translation, however, it speaks directly to Northern Ireland’s conflicts – the decades-long, politically and ethnically fueled clashes over the future of the Nobel Prize winner’s birthplace.

Heaney, who is widely considered one of the most influential poets of his lifetime, was well aware of the global influence he might have on world leaders. And it didn’t take long for his verses to reach the political arena.

Just a few weeks after “The Cure at Troy” opened in the city of Derry, Irish President Mary Robinson quoted the passage on “hope and history” in her inauguration speech. When Bill Clinton visited during the Northern Ireland peace process five years later, he used it too.

By 2000, the line had become famous enough in pop culture that the Irish rock band U2 alluded to it in a song, trusting that their fans would understand the reference.

Stephanie Burt, a literary critic and English professor at Harvard University, told The Washington Post that the play’s multilayered connections to the past explain why its verses have been cited so often by political leaders.

“They establish that our place in history isn’t just in one lifetime or one generation or one year or one century,” she said. “They establish that we and Heaney are a part of a Western history that goes back thousands of years and includes many kinds of stories.”

When one famous leader cites this kind of verse, she added, other figures and speechwriters might borrow it to pen new addresses.

But no one seems to have recited the line as often as Biden.

The former senator quoted it during his 2008 primary campaign, and at the 2013 memorial service for Sean Collier, a police officer killed following the Boston Marathon bombing. He did it again later that year, while addressing U.S.-Korea relations in Seoul, and during a 2014 visit to Cyprus.

When Biden told his daughter Ashley that he would be joining President Barack Obama’s ticket for the White House, she brought up her father’s penchant for those verses.

“You know how you’re always quoting Seamus Heaney about hope and history rhyming?” he remembered her saying over a lunch in 2008. “This is hope and history.”

Burt is quick to note that the passage carries a careful tone that can lend itself to discourse in times of division. While Heaney rose to fame in the 1970s, writing poetry filled with angst and pessimism about the Troubles in Northern Ireland, she said, he gained a much more optimistic outlook by the time he wrote “The Cure at Troy.”

“Things don’t always get better immediately,” she said. “Progress isn’t always preordained or linear, but sometimes things do get better, and times of conflict and sadness can find resting places that are not catastrophic.”

Earlier this year, as election returns on Super Tuesday appeared to put him on the cusp of the Democratic nomination, Biden again turned to Heaney’s “longed-for tidal wave of justice.”

“I truly believe it’s in our power, for the first time in a long time because of what’s happened in the past three years, to make hope and history rhyme,” he said in the March speech in Philadelphia. “That’s what we’re going to do.”

So as soon as he mentioned Seamus Heaney again in his acceptance speech on Thursday, Burt knew the candidate would start speaking about “hope and history” one more time. If the choice of passage was predictable, she said, it was akin to how she compares Biden to other presidential candidates.

“It’s a safe choice,” she said, “but also a good choice.”

The Washington Post’s Matt Viser contributed to this story.