The opening line of the Gettysburg Address invokes the language of the Declaration of Independence. Besides the references to a new nation conceived in liberty and dedicated to the proposition that all men are created equal, Lincoln points us back 87 years ago from 1863 to 1776 (a “score” of years = 20; 4 x 20 + 7 = 87 years).
The opening line of the Gettysburg Address also invokes the language of the Bible, specifically Psalm 90:10. Lincoln was familiar with this passage (see Nov. 21, 1864 letter to John Phillips) and so was most of his audience. Therefore, they would have realized that Lincoln was talking about the Psalmist’s limit on the expected lifetime of man – i.e. somewhere between 70 and 80 years – and that the life of the nation had exceeded the allotted lifetime of man.