That's odd. To me it reads like he doesn't give two shits about slavery either way. His only concern is saving the Union and he would do so at any cost.
Yeah, this the quote they used to teach that the Civil War was about state's rights.
When I was in school, we had to memorize it. Only not the whole thing. Just this part:
"If there be those who would not save the Union unless they could at the same time destroy slavery, I do not agree with them. My paramount object in this struggle is to save the Union, and is not either to save or to destroy slavery."
So they would take the quote out of context and say "See, Lincoln is saying here that he does not care actually care about slavery. He's fighting to keep the South from seceding, so the war was about state rights."
They ignore entirely the rest of the letter where the obvious point is that while Lincoln himself is somewhat indifferent to slavery, he's acknowledging that there's basically no way they can preserve the union without addressing it in some way. In other words, the two sides are beefing over slavery. They are peripherally fighting over state's rights only in the sense that the state right they want to preserve is the right to have slaves. Lincoln himself personally cares more about the union than slavery but he's acknowledging that this is basically what the dispute is about.
They never made us learn the whole letter. They never even told us it existed.
The other quote they always taught us in great detail was Lee saying "In this enlightened age, there are few I believe, but what will acknowledge, that slavery as an institution, is a moral & political evil in any Country. It is useless to expatiate on its disadvantages."
And of course this was to show that Lee was a great man who was personally opposed to slavery but fought for Virginia anyway.
The rest of that quote is "I think it however a greater evil to the white man than to the black race..." which whoops, that right there is a doozy. "... & while my feelings are strongly enlisted in behalf of the latter, my sympathies are more strong for the former. The blacks are immeasurably better off here than in Africa, morally, socially & physically. The painful discipline they are undergoing, is necessary for their instruction as a race, & I hope will prepare & lead them to better things. How long their subjugation may be necessary is known & ordered by a wise Merciful Providence."
In other words, Lee was totally cool with slavery because black people were too stupid to make it on their own, which must be why God entrusted white people with the burden of having to have slaves and maybe someday God will like, make black people smarter and fix it, but until then slavery is the right thing to do.
This thing comes up every time they debate the Confederate statues in Richmond. You have normal people who are totally not racist say "I think it's important we learn from history. Those statues were put up to commemorate a great general, and a great person, and not anything to do with race. So those statues should stay up, but it's fair to provide some additional plaques to provide more commentary." It seems pretty reasonable.
But then you ask them what they want the additional context to be, and it's "That slavery is bad, and it's a vestige of the Confederacy we should not be proud of but that Lee was a great military leader, who heroically fought to preserve state rights and protect Virginia from Northern aggression despite being against slavery." Which is exactly what all of us were taught. They don't get that they're not providing additional objective commentary, they're reinforcing the same stupid myths used to justify those statues in the first place and that have helped preserve racism for a century and a half.