>Slavery was only seized on by Lincoln to provide a moral context.
You are certainly right about that. The “great emancipator” in his own words...
“I will say then that I am not, nor ever have been in favor of bringing about in anyway the social and political equality of the white and black races – that I am not nor ever have been in favor of making voters or jurors of negroes, nor of qualifying them to hold office, nor to intermarry with white people; and I will say in addition to this that there is a physical difference between the white and black races which I believe will forever forbid the two races living together on terms of social and political equality.”
- Abraham Lincoln, 16th US President
Fourth Debate with Stephen A. Douglas at Charleston, Illinois, September 18, 1858
(The Collected Works of Abraham Lincoln edited by Roy P. Basler, Volume III, pp. 145-146.)
Lincoln was the Great Emancipator. The failings of his Emancipation Proclamation were addressed in the 13th Amendment for which he expended great effort and political capital to get enacted.