President Donald Trump honored those who gave their lives while serving the nation in solemn Memorial Day remarks at Arlington National Cemetery – hours after firing off a tweet that drew criticism for focusing on his own accomplishments.

'We strive to be worthy of their sacrifice,' Trump told a crowd of servicemen and women Monday.

Trump acknowledged 'the heroes who rest in these hallowed fields, in cemeteries, battlefields and burial grounds near and far are drawn from the full tapestry of American life.'

'Theirs was a love more deep and more pure than most will ever know,' Trump said. 'They marched into hell so that America could know the blessings of peace.'

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President Donald Trump pauses at the podium as he arrives for a ceremony at the Memorial Amphitheater in Arlington National Cemetery on Memorial Day, Monday, May 28, 2018

Attending the ceremony was Sen. Bob Dole, 94, who recovered from serious injuries in World War II before his long political career, and Navy veteran Ray Chavez, who at 106 is the oldest living survivor of the attack on Pearl Harbor.

'He was in the Oval Office two days ago and he doesn't look a day over 60,' Trump said.

Then Trump singled out seven-year-old Christian Jacobs, who he met last year at Arlington while Jacobs was wearing a full Marine dress uniform in tribute to his late father, Marine Sgt. Christopher Jacobs.

'Christian walked over to me with great confidence, shook my hand, looked me straight in the eye and asked if I would like to meet his dad,' Trump told the audience, recalling the emotional visit from last year.

'Christian, I want you to know that even though your father has left this world,' Trump said, addressing his remarks to the boy in the audience. 'He's left it for the next. But he's not gone, he'll never be gone. Your dad's love, courage, and strength live in you, Christian.'

Trump also spoke of Marine Lt. Col. David Greene, a reservist who became the highest ranking Marine to die in Iraq in 2004. Trump told his widow, Sarah:

'He's looking down on you right now you know that? Right? He's looking down on you and he's so proud and happy,' Trump said.

President Trump laid a wreath at the tomb of the unknown soldier

Trump addressed comments to seven-year-old Christian Jacobs, who he met last year at Arlington while Jacobs was wearing a full Marine dress uniform in tribute to his late father, Marine Sgt. Christopher Jacobs

Earlier, Trump wished the nation a 'Happy Memorial Day!' as Americans began honoring fallen heroes on a popular three-day weekend – then touted the 'best economy' in decades.

Trump, who prepared to make his second trip to Arlington National Cemetery for a Memorial Day ceremony, also said the fallen 'would be very happy and proud' about how the nation is doing.

'Happy Memorial Day! Those who died for our great country would be very happy and proud at how well our country is doing today,' Trump wrote on Twitter Monday morning.

Trump's speech was about military sacrifice, but he took heat online for his tweet about economic and employment gains on his watch

President Donald Trump lays a wreath at the Tomb of the Unknown Solider at Arlington National Cemetery, Monday, May 28, 2018

'Happy Memorial Day!' President Trump wrote on twitter as the nation prepared to honor those who gave their lives in military service to their country

Then he switched to strong economic statistics. 'Best economy in decades, lowest unemployment numbers for Blacks and Hispanics EVER (& women in 18years), rebuilding our Military and so much more. Nice!' the president wrote.

Trump also released a video where he spoke directly to the camera and recalled his encounter with a young boy name Christian Jacobs, who was wearing a full dress military uniform while standing by his father's graveside.

'I know that everybody is remembering the fallen soldiers who paid the ultimate price for our country,' he wrote.

Jacobs' father, Marine Sgt. Christopher Jacobs, died in 2011 during a military training exercise.

Trump's tweet touting the economic achievements of his presidency took a different tone than other senior officials.

Trump also hailed the economy and employment gains

The president released a video recounting last year's ceremony

Sen. John McCain, a Navy veteran who is battling brain cancer and is the subject of a new laudatory documentary, wrote on Twitter: 'Today we honor the Americans who sacrificed everything to secure the blessings of liberty. Family and friends to some, heroes to all - who lived, fought and died for the safety and future of a great and good nation. God bless them and grant them perpetual peace. #MemorialDay.'

Trump's secretary of state, Mike Pompeo, wrote: 'On this #MemorialDay, we remember all the men and women in uniform who've given their lives for our nation. We are forever grateful for their sacrifice. Our prayers are with their loved ones.'

First Lady Melania Trump wrote: On #MemorialDay we honor the many Americans who laid down their lives for our great country. As one nation under God, we come together to remember that freedom isn’t free. Thank you to all the service members & their families who sacrifice so much to keep us safe.'

Trump heads to Arlington Monday morning to attend Memorial Day ceremonies.

SACRIFICE: Ailing Arizona Sen. John McCain acknowledged those who 'sacrificed everything'

DIPLOMATIC: Secretary of State Mike Pompeo said the nation was 'forever grateful'

ONE NATION: First Lady Melania Trump thanked living service members while honoring 'those who laid down their lives for our great country'

President Trump released a video of his visit to Arlington National Cemetery last year