Which brings us back to the original question of what power he had to set the slaves free in areas not in rebellion. Lincoln's view can be seen in the lines you quoted above about the Corwin Amendment: "“I understand a proposed amendment to the Constitution has passed Congress, to the effect that the Federal Government shall never interfere with the domestic institutions of the States, including that of persons held to service. Holding such a provision to now be implied constitutional law, I have no objection to its being made express and irrevocable.”
Lincoln didn't think he had the constitutional authority to end slavery in areas not in rebellion. That's why he pushed for the 13th Amendment.
That quote is from before the war. If he had told people what powers he would exercise once the war started, he would have been run out of office.
Regarding Lincoln’s comment on slavery, he is obviously right. It was permitted under the Constitution, although not expressly. But there is nothing in the Constitution that gave him the power to emancipate slaves, smash printing presses and shut papers down, suspend habeas corpus, deport Congressmen, etc. Once the war started, Lincoln ignored the Constitution, even the Jaffaites acknowledge that. My point was NOT that Lincoln didn’t really oppose slavery - he clearly did. What I have said is that ending slavery was at best a secondary issue for him. If it had been, he would have, on principle, refused to support the Corwin Amendment because it represented something reprehensible.