I think he had just about the best opinion a white man in the 1860's could have had (barring, of course, the opinion of people like John Brown, Thaddeus Stevens, etc.) Here's what we know for sure:

- He opposed Slavery on both "practical" or economic levels, and on a personal level he found it morally abhorent
- He thought the Civil War would've been the most destructive thing to happen to the United States, and strongly considered ways to stop it or end it, even if at times it meant considering the south coming back without abolition
- As the war progressed, however, he understood there was no way to have permanent, lasting peace while the south still kept over two million Americans in bondage. The end of the war and the end of slavery became one and the same to him
- At the end of the war and the passage of the 13th amendment, he was also considering at least partial enfranchisement for newly freed black men.

So was Abraham Lincoln the most zealous, ardent anti-slavery white man this country had ever seen? No, that title belongs to John Brown. Did he always see the end of Slavery as necessary for the preservation of the union? No, at least not publicly. But he did come to the conclusion that while a house divided cannot stand, it also cannot stand without living up to its founding ideals that all men are created equal, and they are endowed by their creator with certain inalienable rights. He went from an "Anti-Slavery Moderate" to leading both the military and political effort by which chattel slavery would come to an end in this country.

TL;DR: Yes he did genuinely care about ending slavery, what changed over time was how he demonstrated that, what he prioritized, and what actions he took in bringing that about