In a video released Friday, President Biden reflected on the Sept. 11, 2001, terrorist attacks in America, insisting that "national unity" is America's "greatest strength."

Biden opened the video by discussing his friend Davis, whom Biden said he "grew up with in Delaware."

"On this day, 20 years ago, he and his family had just passed the first year without their youngest of three sons, Teddy, who died in a boating accident at age 15," Biden said as he began to describe one family's horror on that day. "His eldest son, Davis Jr., was just six days into a new job on the 104th floor of the South Tower of the World Trade Center."

Following the attacks, Biden said he and Davis talked "as fathers who know" about the tragedy which resulted in his son's death. 

"I was on my way to speak to students at the University of Delaware about what to make of the new world we were in. He told me to tell people, 'Don't be afraid,'" Biden said. "The absolute courage it took after two unimaginable losses is extraordinary."

"To the families of the 2,977 people from more than 90 nations killed on September 11, 2001, in New York City, Arlington, Virginia, and Shanksville, Pennsylvania, and the thousands of more that were injured, America and the world commemorate you and your loved ones," Biden said in the video.

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

"But it's so hard, whether it's the first year or the 20th," Biden continued. "Children have grown up without parents, and parents have suffered without children. Husbands and wives have had to find ways forward without their partners in their life with them … No matter how much time has passed, these commemorations bring everything painfully back as if you just got the news a few days ago."

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"In the days that followed September 11, 2001, we saw heroism everywhere," Biden stated. "We also saw something all too rare: national unity.

"Unity is what makes us who we are, America at its best," Biden said. "To me, that's the central lesson of September 11th."

In noting unity, Biden said he has also witnessed the "dark side of human nature" over "fear and anger, resentment and violence against Muslim Americans, true and faithful followers of a peaceful religion."

Biden on Saturday will attend memorial events at all three sites where planes crashed on 9/11: in New York City, at the Pentagon in Arlington, Virginia, and in Shanksville, Pennsylvania.