Jaffa put it like this, in a paragraph that distills Lincoln’s mind better than any words not written by Lincoln himself.

If self-government was a right, and not a mere fact characterizing the American scene (more or less), then it must be derived from some primary source of obligation. There must be something, Lincoln insisted, inhering in each man, as a man, which created an obligation in every other man. And if any majority anywhere, however constituted, might rightfully enslave any man or men, it could only be because there was nothing in any man which, simply because he was a man, other men were bound to respect.

Saving President Lincoln | The Weekly Standard.