"I've never stood anyplace on earth where it's easier to be humbled than here," said Spielberg, whose biopic about the 16th president, "Lincoln," is currently in theaters.
About 9,000 people attended the event near the site where Lincoln gave the famous speech during the Civil War.
"Their sacrifice of nearly 150 years ago was so complete and so completely essential that time, as Lincoln predicted, hasn't been able to erase it from memory," Spielberg said.
The two-time Academy Award-winning director spent seven years working on "Lincoln." He said the president came to feel like one of his oldest and dearest friends. The filmmaker called the "Gettysburg Address" the single "most perfect prose poem ever penned by an American."
"Lincoln wanted us to understand that equality was a small 'D' democratic essential," Spielberg said.
The crowd gave Spielberg a standing ovation. As part of the event, 16 newly minted Americans from 11 countries took the oath of allegiance to become U.S. citizens.
The Associated Press contributed to this report.