What famous speech did Abraham Lincoln deliver that emphasized the commitment to the principle of human equality?

The Gettysburg Address is a pivotal speech delivered by Abraham Lincoln on November 19, 1863, during the dedication of the Soldiers' National Cemetery in Gettysburg, Pennsylvania. In this iconic address, Lincoln reaffirmed the principles of human equality stated in the Declaration of Independence. He emphasized that the Civil War was a test of the nation's commitment to those principles, particularly the idea that all men are created equal.

Lincoln's remarks were succinct yet powerful, calling for a "new birth of freedom" and the assurance that democracy would endure. He articulated a vision of the nation not just as a political entity but as a collective realization of human rights. This speech has since become one of the most celebrated orations in American history, symbolizing the struggle for equality and the sacrifices made during the Civil War.

The other options, while significant in their own right, do not carry the same direct emphasis on human equality as the Gettysburg Address. The Emancipation Proclamation primarily focused on the abolition of slavery, the Second Inaugural Address addressed reconciliation, and the letter to Congress is less well-known and does not specifically highlight the principle of human equality in the same manner.