"I've never stood anyplace on earth where it's easier to be humbled than here," said Spielberg, whose biopic about the 16th president is currently in theaters.
His remarks were made at the annual event at the Soldier's National Cemetery in Gettysburg, near the site where Lincoln gave the famous oration amid the American Civil War in 1863, four months after the battle in which the Union turned back an invasion of the North by Confederate troops under Gen. Robert E. Lee.
After spending seven years working his new movie "Lincoln," Spielberg said the president came to feel like one of his oldest and dearest friends, and he sensed he was living in the presence of what he called Lincoln's "eloquent ghost."
"Lincoln wanted us to understand that equality was a small 'D' democratic essential," Spielberg said, describing Lincoln's three-minute speech as "his best and truest voice" and the single "most perfect prose poem ever penned by an American."
Carl Sandberg, in his biography of Lincoln, described it as a speech about how democracy is worth fighting for.
"It had the dream touch of vast and furious events epitomized for any foreteller to read what was to come," Sandberg wrote. "His cadences sang the ancient song that where there is freedom men have fought and sacrificed for it, and that freedom is worth men's dying for."
As part of the event, 16 newly minted Americans from 11 countries took the oath of allegiance to become U.S. citizens.
Spielberg spoke of the interplay between history and memory, and between memory and justice.
"It's the hunger we feel for coherence, it's the hunger we feel for progress for a better world," he said. "I think justice and memory are inseparable."
The crowd, estimated at 9,000, gave him a standing ovation.
Penn State film major Alison Golanoski, 19, from Gettysburg, said afterward that Spielberg's passion for Lincoln came through.
"He was very invested in Lincoln as a person, and his personality," Golanoski said. "I loved all of it."
The 150th year since the battle will be marked in 2013, particularly around the battle's anniversary in early July.
"Lincoln," which stars Daniel Day-Lewis in the title role, concentrates on the period leading up to the president's assassination in 1865.