President Biden on Friday released a lengthy video message to commemorate the 20th anniversary of the 9/11 attacks, calling for unity in a divided country and acknowledging that the pain and grief from that day may not have dulled for some families, even after two decades.

Standing in the White House in a dark suit, with a blurred out American flag visible over his shoulder, Biden spoke somberly and expressed condolences from himself and first lady Jill Biden to the loved ones of the nearly 3,000 people killed after terrorist-hijacked planes crashed that day into the World Trade Center in New York; into the Pentagon in Arlington; and into a field in Shanksville, Pa.

“To the families of the 2,977 people, from more than 90 nations, killed on Sept. 11, 2001, … and 1,000 more who were injured, America and the world commemorate you and your loved ones, the pieces of your soul,” Biden said.

“We honor all those who are risked and gave their lives in the minutes, hours, months and years afterwards,” Biden added. “The firefighters, police officers, EMTs and construction workers, the doctors and nurses, faith leaders, service members, veterans, and all the everyday people who gave their all to rescue, recover and rebuild.”

Biden opened by recalling a friend from Delaware named Davis, who on Sept. 11, 2001, had just passed his first year after the loss of his 15-year-old son in a boating accident. Davis’s eldest son, Davis Jr., was then only six days into his new job on the 104th floor of the South Tower of the World Trade Center.

After the towers fell, Davis headed straight for Ground Zero to search for his missing son, Biden said.

“They searched deep into the last inning of hope, as he put it,” the president said.

A few days after the attacks, Biden said he spoke with Davis “as fathers who know,” a reference to the loss of his infant daughter Naomi in a 1972 car accident that also killed Biden’s first wife.

Biden was on his way to speak to students at the University of Delaware “about what to make of the new world,” he said, when Davis gave him some advice.

“He said, ‘Tell them don’t be afraid,’ ” Biden said.

Biden marveled at that advice.

“The absolute courage it took after two unimaginable losses is extraordinary, yet the most ordinary of American things,” Biden said. “To know life can be unfair and uncertain, a cruel twist of accident, or a deliberate act of evil — but even in darkness, to still be the light.”

Biden also invoked memories of the “true sense of national unity” that he said Americans saw in the days that followed Sept. 11, 2001, and, without mention of the 20-year war in Afghanistan that his administration just ended, honored “the 9/11 generation” that stepped up “to serve and protect in the face of terror, to get those terrorists who were responsible” for the attacks.

Biden also acknowledged that, following 9/11, Americans also witnessed “the darker forces of human nature: fear and anger, resentment and violence against Muslim Americans, true and faithful followers of a peaceful religion.”

He called unity the central tenet of America at its best, and said that while it has bent, it must never break. Unity did not, he noted, have to mean everyone believed the same thing, but it did require that Americans have “a fundamental respect and faith in each other.”

“To me, that’s the central lesson of Sept. 11th, is that at our most vulnerable — the push and pull of all that makes us human, and the battle for the soul of America — unity is our greatest strength,” Biden said.

“We find strength in its broken places, as Hemingway wrote. We find light in the darkness. We find purpose to repair, renew and rebuild. And as my friend told me that September, 20 years ago: We must not be afraid.”