Just hours before they are to be sworn into office, President-elect Joe Biden and Vice President-elect Kamala Harris honored the 400,000 Americans who have died as a result of the novel coronavirus with a tribute in front of the Lincoln Memorial Reflecting Pool.

After an invocation, Harris called on Americans to stand together.

"For many months we have grieved by ourselves. Tonight we grieve and begin healing together. Though we may be physically separated, we, the American people, are united in spirit," she said.

Biden thanked the country's nurses and also echoed the call for unity.

"To heal we must remember, and it’s hard sometimes to remember, but that’s how we heal," he said.

As the ceremony ended, 400 lights along the pool were lit up, symbolizing the lives lost. Church bells around the country rang in unison and gospel singer Yolanda Adams sang Leonard Cohen's "Hallelujah."

The White House has released a pre-taped farewell address from President Trump on his final full day in office.

"We did what we came here to do – and so much more," Trump said, speaking from scripted remarks directly into the camera and standing behind a lectern with the presidential seal. "This week, we inaugurate a new administration and pray for its success in keeping America safe and prosperous. We extend our best wishes, and we also want them to have luck -- a very important word."

Trump thanked several people, including Vice President Mike Pence.

"Most of all, I want to thank the American people," Trump said. "To serve as your president has been an honor beyond description. Thank you for this extraordinary privilege."

Trump then condemned the riot at the Capitol and called on Americans to "unite around our shared values."

"All Americans were horrified by the assault on our Capitol. Political violence is an attack on everything we cherish as Americans. It can never be tolerated," Trump said.

He warned that the greatest danger the country faces as he leaves office is "a loss of confidence in our national greatness" -- going on to talk about the shared "heritage" of the country under threat and condemning "political censorship and blacklisting."

"Now, as I prepare to hand power over to a new administration at noon on Wednesday, I want you to know that the movement we started is only just beginning," he said, closing out the 20-minute farewell address.

Vice President Mike Pence will not be attending Trump’s farewell ceremony at Joint Base Andrews on Wednesday, according to his schedule.

Instead, his only event of the day is to attend Biden's inauguration.

-ABC News' Elizabeth Thomas

Biden and future first lady Jill Biden arrived at Joint Base Andrews shortly before 4 p.m. Tuesday.

They boarded their flight to Washington, D.C., from New Castle County Airport in Delaware and departed shortly after 3 p.m.

In Washington, the Bidens, as well as Vice President-elect Kamala Harris and her husband, Doug Emhoff, will take part in a national COVID-19 memorial service at the Lincoln Memorial Tuesday evening to honor the 400,000 Americans who have lost their lives to the virus.

-ABC News' Molly Nagle and Ben Gittleson