Lincoln really didn’t care about slavery one way or the other - he stated so - until he realized he could use it for political gain. He supported the original 13th amendment - The Corwin amendment. Read it.
There are a couple of schools of thought on that, and I swear they both have good arguments. That they have an open season is due very much to the secretive nature of their subject, who it seems never let anyone close to what he really thought or valued. Even Wm. Herndon and his own wife found him perplexing, two people who knew him best -- but even they confess that really, they didn't.
That leaves us to infer intentions from actions and outcomes. And that is a slow, laborious, and argumentative process that can, absent the discovery of some hitherto-unknown text, run very easily for another 300 years.