why does lincoln begin his eulogy to the soldiers buried at gettysburing with "four score and secen years ago"?

Abraham Lincoln began his famous Gettysburg Address with the phrase "Four score and seven years ago" to reference the time that had passed since the founding of the United States. In using this phrase, Lincoln was establishing a historical context, starting with the year 1776, when the Declaration of Independence was adopted.

"Four score and seven years ago" equals eighty-seven years and Lincoln was delivering his address in 1863. By starting with this phrase, he was drawing a direct connection between the ideals of the Declaration of Independence and the current struggle of the Civil War, emphasizing the nation's founding principles of liberty, equality and self-government. Lincoln sought to remind the audience of the country's founding and to invoke a sense of unity and commitment to preserving the Union and the principles for which it stood.